text: //                 ______  _____                 ______                _________
  //  ______________ ___  /_ ___(_)_______         ___  /_ ______ ______ ______  /
  //  __  ___/_  __ \__  __ \__  / __  __ \        __  __ \_  __ \_  __ \_  __  /
  //  _  /    / /_/ /_  /_/ /_  /  _  / / /        _  / / // /_/ // /_/ // /_/ /
  //  /_/     \____/ /_.___/ /_/   /_/ /_/ ________/_/ /_/ \____/ \____/ \__,_/
  //                                      _/_____/
  //
  // Fast & memory efficient hashtable based on robin hood hashing for C++11/14/17/20
  // https://github.com/martinus/robin-hood-hashing
  //
  // Licensed under the MIT License <http://opensource.org/licenses/MIT>.
  // SPDX-License-Identifier: MIT
  // Copyright (c) 2018-2021 Martin Ankerl <http://martin.ankerl.com>
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in all
  // copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  // SOFTWARE.
  
  #ifndef ROBIN_HOOD_H_INCLUDED
  #define ROBIN_HOOD_H_INCLUDED
  
  // see https://semver.org/
  #define ROBIN_HOOD_VERSION_MAJOR 3  // for incompatible API changes
  #define ROBIN_HOOD_VERSION_MINOR 11 // for adding functionality in a backwards-compatible manner
  #define ROBIN_HOOD_VERSION_PATCH 2  // for backwards-compatible bug fixes
  
  #include <algorithm>
  #include <cstdlib>
  #include <cstring>
  #include <functional>
  #include <limits>
  #include <memory> // only to support hash of smart pointers
  #include <stdexcept>
  #include <string>
  #include <type_traits>
  #include <utility>
  #if __cplusplus >= 201703L
  #    include <string_view>
  #endif
  
  // #define ROBIN_HOOD_LOG_ENABLED
  #ifdef ROBIN_HOOD_LOG_ENABLED
  #    include <iostream>
  #    define ROBIN_HOOD_LOG(...) \
          std::cout << __FUNCTION__ << "@" << __LINE__ << ": " << __VA_ARGS__ << std::endl;
  #else
  #    define ROBIN_HOOD_LOG(x)
  #endif
  
  // #define ROBIN_HOOD_TRACE_ENABLED
  #ifdef ROBIN_HOOD_TRACE_ENABLED
  #    include <iostream>
  #    define ROBIN_HOOD_TRACE(...) \
          std::cout << __FUNCTION__ << "@" << __LINE__ << ": " << __VA_ARGS__ << std::endl;
  #else
  #    define ROBIN_HOOD_TRACE(x)
  #endif
  
  // #define ROBIN_HOOD_COUNT_ENABLED
  #ifdef ROBIN_HOOD_COUNT_ENABLED
  #    include <iostream>
  #    define ROBIN_HOOD_COUNT(x) ++counts().x;
  namespace robin_hood {
  struct Counts {
      uint64_t shiftUp{};
      uint64_t shiftDown{};
  };
  inline std::ostream& operator<<(std::ostream& os, Counts const& c) {
      return os << c.shiftUp << " shiftUp" << std::endl << c.shiftDown << " shiftDown" << std::endl;
  }
  
  static Counts& counts() {
      static Counts counts{};
      return counts;
  }
  } // namespace robin_hood
  #else
  #    define ROBIN_HOOD_COUNT(x)
  #endif
  
  // all non-argument macros should use this facility. See
  // https://www.fluentcpp.com/2019/05/28/better-macros-better-flags/
  #define ROBIN_HOOD(x) ROBIN_HOOD_PRIVATE_DEFINITION_##x()
  
  // mark unused members with this macro
  #define ROBIN_HOOD_UNUSED(identifier)
  
  // bitness
  #if SIZE_MAX == UINT32_MAX
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_BITNESS() 32
  #elif SIZE_MAX == UINT64_MAX
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_BITNESS() 64
  #else
  #    error Unsupported bitness
  #endif
  
  // endianess
  #ifdef _MSC_VER
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_LITTLE_ENDIAN() 1
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_BIG_ENDIAN() 0
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_LITTLE_ENDIAN() \
          (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_BIG_ENDIAN() (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
  #endif
  
  // inline
  #ifdef _MSC_VER
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_NOINLINE() __declspec(noinline)
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_NOINLINE() __attribute__((noinline))
  #endif
  
  // exceptions
  #if !defined(__cpp_exceptions) && !defined(__EXCEPTIONS) && !defined(_CPPUNWIND)
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_EXCEPTIONS() 0
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_EXCEPTIONS() 1
  #endif
  
  // count leading/trailing bits
  #if !defined(ROBIN_HOOD_DISABLE_INTRINSICS)
  #    ifdef _MSC_VER
  #        if ROBIN_HOOD(BITNESS) == 32
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_BITSCANFORWARD() _BitScanForward
  #        else
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_BITSCANFORWARD() _BitScanForward64
  #        endif
  #        include <intrin.h>
  #        pragma intrinsic(ROBIN_HOOD(BITSCANFORWARD))
  #        define ROBIN_HOOD_COUNT_TRAILING_ZEROES(x)                                       \
              [](size_t mask) noexcept -> int {                                             \
                  unsigned long index;                                                      \
                  return ROBIN_HOOD(BITSCANFORWARD)(&index, mask) ? static_cast<int>(index) \
                                                                  : ROBIN_HOOD(BITNESS);    \
              }(x)
  #    else
  #        if ROBIN_HOOD(BITNESS) == 32
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_CTZ() __builtin_ctzl
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_CLZ() __builtin_clzl
  #        else
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_CTZ() __builtin_ctzll
  #            define ROBIN_HOOD_PRIVATE_DEFINITION_CLZ() __builtin_clzll
  #        endif
  #        define ROBIN_HOOD_COUNT_LEADING_ZEROES(x) ((x) ? ROBIN_HOOD(CLZ)(x) : ROBIN_HOOD(BITNESS))
  #        define ROBIN_HOOD_COUNT_TRAILING_ZEROES(x) ((x) ? ROBIN_HOOD(CTZ)(x) : ROBIN_HOOD(BITNESS))
  #    endif
  #endif
  
  // fallthrough
  #ifndef __has_cpp_attribute // For backwards compatibility
  #    define __has_cpp_attribute(x) 0
  #endif
  #if __has_cpp_attribute(clang::fallthrough)
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH() [[clang::fallthrough]]
  #elif __has_cpp_attribute(gnu::fallthrough)
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH() [[gnu::fallthrough]]
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH()
  #endif
  
  // likely/unlikely
  #ifdef _MSC_VER
  #    define ROBIN_HOOD_LIKELY(condition) condition
  #    define ROBIN_HOOD_UNLIKELY(condition) condition
  #else
  #    define ROBIN_HOOD_LIKELY(condition) __builtin_expect(condition, 1)
  #    define ROBIN_HOOD_UNLIKELY(condition) __builtin_expect(condition, 0)
  #endif
  
  // detect if native wchar_t type is availiable in MSVC
  #ifdef _MSC_VER
  #    ifdef _NATIVE_WCHAR_T_DEFINED
  #        define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 1
  #    else
  #        define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 0
  #    endif
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 1
  #endif
  
  // detect if MSVC supports the pair(std::piecewise_construct_t,...) consructor being constexpr
  #ifdef _MSC_VER
  #    if _MSC_VER <= 1900
  #        define ROBIN_HOOD_PRIVATE_DEFINITION_BROKEN_CONSTEXPR() 1
  #    else
  #        define ROBIN_HOOD_PRIVATE_DEFINITION_BROKEN_CONSTEXPR() 0
  #    endif
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_BROKEN_CONSTEXPR() 0
  #endif
  
  // workaround missing "is_trivially_copyable" in g++ < 5.0
  // See https://stackoverflow.com/a/31798726/48181
  #if defined(__GNUC__) && __GNUC__ < 5
  #    define ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(...) __has_trivial_copy(__VA_ARGS__)
  #else
  #    define ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(...) std::is_trivially_copyable<__VA_ARGS__>::value
  #endif
  
  // helpers for C++ versions, see https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html
  #define ROBIN_HOOD_PRIVATE_DEFINITION_CXX() __cplusplus
  #define ROBIN_HOOD_PRIVATE_DEFINITION_CXX98() 199711L
  #define ROBIN_HOOD_PRIVATE_DEFINITION_CXX11() 201103L
  #define ROBIN_HOOD_PRIVATE_DEFINITION_CXX14() 201402L
  #define ROBIN_HOOD_PRIVATE_DEFINITION_CXX17() 201703L
  
  #if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX17)
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_NODISCARD() [[nodiscard]]
  #else
  #    define ROBIN_HOOD_PRIVATE_DEFINITION_NODISCARD()
  #endif
  
  namespace robin_hood {
  
  #if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX14)
  #    define ROBIN_HOOD_STD std
  #else
  
  // c++11 compatibility layer
  namespace ROBIN_HOOD_STD {
  template <class T>
  struct alignment_of
      : std::integral_constant<std::size_t, alignof(typename std::remove_all_extents<T>::type)> {};
  
  template <class T, T... Ints>
  class integer_sequence {
  public:
      using value_type = T;
      static_assert(std::is_integral<value_type>::value, "not integral type");
      static constexpr std::size_t size() noexcept {
          return sizeof...(Ints);
      }
  };
  template <std::size_t... Inds>
  using index_sequence = integer_sequence<std::size_t, Inds...>;
  
  namespace detail_ {
  template <class T, T Begin, T End, bool>
  struct IntSeqImpl {
      using TValue = T;
      static_assert(std::is_integral<TValue>::value, "not integral type");
      static_assert(Begin >= 0 && Begin < End, "unexpected argument (Begin<0 || Begin<=End)");
  
      template <class, class>
      struct IntSeqCombiner;
  
      template <TValue... Inds0, TValue... Inds1>
      struct IntSeqCombiner<integer_sequence<TValue, Inds0...>, integer_sequence<TValue, Inds1...>> {
          using TResult = integer_sequence<TValue, Inds0..., Inds1...>;
      };
  
      using TResult =
          typename IntSeqCombiner<typename IntSeqImpl<TValue, Begin, Begin + (End - Begin) / 2,
                                                      (End - Begin) / 2 == 1>::TResult,
                                  typename IntSeqImpl<TValue, Begin + (End - Begin) / 2, End,
                                                      (End - Begin + 1) / 2 == 1>::TResult>::TResult;
  };
  
  template <class T, T Begin>
  struct IntSeqImpl<T, Begin, Begin, false> {
      using TValue = T;
      static_assert(std::is_integral<TValue>::value, "not integral type");
      static_assert(Begin >= 0, "unexpected argument (Begin<0)");
      using TResult = integer_sequence<TValue>;
  };
  
  template <class T, T Begin, T End>
  struct IntSeqImpl<T, Begin, End, true> {
      using TValue = T;
      static_assert(std::is_integral<TValue>::value, "not integral type");
      static_assert(Begin >= 0, "unexpected argument (Begin<0)");
      using TResult = integer_sequence<TValue, Begin>;
  };
  } // namespace detail_
  
  template <class T, T N>
  using make_integer_sequence = typename detail_::IntSeqImpl<T, 0, N, (N - 0) == 1>::TResult;
  
  template <std::size_t N>
  using make_index_sequence = make_integer_sequence<std::size_t, N>;
  
  template <class... T>
  using index_sequence_for = make_index_sequence<sizeof...(T)>;
  
  } // namespace ROBIN_HOOD_STD
  
  #endif
  
  namespace detail {
  
  // make sure we static_cast to the correct type for hash_int
  #if ROBIN_HOOD(BITNESS) == 64
  using SizeT = uint64_t;
  #else
  using SizeT = uint32_t;
  #endif
  
  template <typename T>
  T rotr(T x, unsigned k) {
      return (x >> k) | (x << (8U * sizeof(T) - k));
  }
  
  // This cast gets rid of warnings like "cast from 'uint8_t*' {aka 'unsigned char*'} to
  // 'uint64_t*' {aka 'long unsigned int*'} increases required alignment of target type". Use with
  // care!
  template <typename T>
  inline T reinterpret_cast_no_cast_align_warning(void* ptr) noexcept {
      return reinterpret_cast<T>(ptr);
  }
  
  template <typename T>
  inline T reinterpret_cast_no_cast_align_warning(void const* ptr) noexcept {
      return reinterpret_cast<T>(ptr);
  }
  
  // make sure this is not inlined as it is slow and dramatically enlarges code, thus making other
  // inlinings more difficult. Throws are also generally the slow path.
  template <typename E, typename... Args>
  [[noreturn]] ROBIN_HOOD(NOINLINE)
  #if ROBIN_HOOD(HAS_EXCEPTIONS)
      void doThrow(Args&&... args) {
      // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-array-to-pointer-decay)
      throw E(std::forward<Args>(args)...);
  }
  #else
      void doThrow(Args&&... ROBIN_HOOD_UNUSED(args) /*unused*/) {
      abort();
  }
  #endif
  
  template <typename E, typename T, typename... Args>
  T* assertNotNull(T* t, Args&&... args) {
      if (ROBIN_HOOD_UNLIKELY(nullptr == t)) {
          doThrow<E>(std::forward<Args>(args)...);
      }
      return t;
  }
  
  template <typename T>
  inline T unaligned_load(void const* ptr) noexcept {
      // using memcpy so we don't get into unaligned load problems.
      // compiler should optimize this very well anyways.
      T t;
      std::memcpy(&t, ptr, sizeof(T));
      return t;
  }
  
  // Allocates bulks of memory for objects of type T. This deallocates the memory in the destructor,
  // and keeps a linked list of the allocated memory around. Overhead per allocation is the size of a
  // pointer.
  template <typename T, size_t MinNumAllocs = 4, size_t MaxNumAllocs = 256>
  class BulkPoolAllocator {
  public:
      BulkPoolAllocator() noexcept = default;
  
      // does not copy anything, just creates a new allocator.
      BulkPoolAllocator(const BulkPoolAllocator& ROBIN_HOOD_UNUSED(o) /*unused*/) noexcept
          : mHead(nullptr)
          , mListForFree(nullptr) {}
  
      BulkPoolAllocator(BulkPoolAllocator&& o) noexcept
          : mHead(o.mHead)
          , mListForFree(o.mListForFree) {
          o.mListForFree = nullptr;
          o.mHead = nullptr;
      }
  
      BulkPoolAllocator& operator=(BulkPoolAllocator&& o) noexcept {
          reset();
          mHead = o.mHead;
          mListForFree = o.mListForFree;
          o.mListForFree = nullptr;
          o.mHead = nullptr;
          return *this;
      }
  
      BulkPoolAllocator&
      // NOLINTNEXTLINE(bugprone-unhandled-self-assignment,cert-oop54-cpp)
      operator=(const BulkPoolAllocator& ROBIN_HOOD_UNUSED(o) /*unused*/) noexcept {
          // does not do anything
          return *this;
      }
  
      ~BulkPoolAllocator() noexcept {
          reset();
      }
  
      // Deallocates all allocated memory.
      void reset() noexcept {
          while (mListForFree) {
              T* tmp = *mListForFree;
              ROBIN_HOOD_LOG("std::free")
              std::free(mListForFree);
              mListForFree = reinterpret_cast_no_cast_align_warning<T**>(tmp);
          }
          mHead = nullptr;
      }
  
      // allocates, but does NOT initialize. Use in-place new constructor, e.g.
      //   T* obj = pool.allocate();
      //   ::new (static_cast<void*>(obj)) T();
      T* allocate() {
          T* tmp = mHead;
          if (!tmp) {
              tmp = performAllocation();
          }
  
          mHead = *reinterpret_cast_no_cast_align_warning<T**>(tmp);
          return tmp;
      }
  
      // does not actually deallocate but puts it in store.
      // make sure you have already called the destructor! e.g. with
      //  obj->~T();
      //  pool.deallocate(obj);
      void deallocate(T* obj) noexcept {
          *reinterpret_cast_no_cast_align_warning<T**>(obj) = mHead;
          mHead = obj;
      }
  
      // Adds an already allocated block of memory to the allocator. This allocator is from now on
      // responsible for freeing the data (with free()). If the provided data is not large enough to
      // make use of, it is immediately freed. Otherwise it is reused and freed in the destructor.
      void addOrFree(void* ptr, const size_t numBytes) noexcept {
          // calculate number of available elements in ptr
          if (numBytes < ALIGNMENT + ALIGNED_SIZE) {
              // not enough data for at least one element. Free and return.
              ROBIN_HOOD_LOG("std::free")
              std::free(ptr);
          } else {
              ROBIN_HOOD_LOG("add to buffer")
              add(ptr, numBytes);
          }
      }
  
      void swap(BulkPoolAllocator<T, MinNumAllocs, MaxNumAllocs>& other) noexcept {
          using std::swap;
          swap(mHead, other.mHead);
          swap(mListForFree, other.mListForFree);
      }
  
  private:
      // iterates the list of allocated memory to calculate how many to alloc next.
      // Recalculating this each time saves us a size_t member.
      // This ignores the fact that memory blocks might have been added manually with addOrFree. In
      // practice, this should not matter much.
      ROBIN_HOOD(NODISCARD) size_t calcNumElementsToAlloc() const noexcept {
          auto tmp = mListForFree;
          size_t numAllocs = MinNumAllocs;
  
          while (numAllocs * 2 <= MaxNumAllocs && tmp) {
              auto x = reinterpret_cast<T***>(tmp);
              tmp = *x;
              numAllocs *= 2;
          }
  
          return numAllocs;
      }
  
      // WARNING: Underflow if numBytes < ALIGNMENT! This is guarded in addOrFree().
      void add(void* ptr, const size_t numBytes) noexcept {
          const size_t numElements = (numBytes - ALIGNMENT) / ALIGNED_SIZE;
  
          auto data = reinterpret_cast<T**>(ptr);
  
          // link free list
          auto x = reinterpret_cast<T***>(data);
          *x = mListForFree;
          mListForFree = data;
  
          // create linked list for newly allocated data
          auto* const headT =
              reinterpret_cast_no_cast_align_warning<T*>(reinterpret_cast<char*>(ptr) + ALIGNMENT);
  
          auto* const head = reinterpret_cast<char*>(headT);
  
          // Visual Studio compiler automatically unrolls this loop, which is pretty cool
          for (size_t i = 0; i < numElements; ++i) {
              *reinterpret_cast_no_cast_align_warning<char**>(head + i * ALIGNED_SIZE) =
                  head + (i + 1) * ALIGNED_SIZE;
          }
  
          // last one points to 0
          *reinterpret_cast_no_cast_align_warning<T**>(head + (numElements - 1) * ALIGNED_SIZE) =
              mHead;
          mHead = headT;
      }
  
      // Called when no memory is available (mHead == 0).
      // Don't inline this slow path.
      ROBIN_HOOD(NOINLINE) T* performAllocation() {
          size_t const numElementsToAlloc = calcNumElementsToAlloc();
  
          // alloc new memory: [prev |T, T, ... T]
          size_t const bytes = ALIGNMENT + ALIGNED_SIZE * numElementsToAlloc;
          ROBIN_HOOD_LOG("std::malloc " << bytes << " = " << ALIGNMENT << " + " << ALIGNED_SIZE
                                        << " * " << numElementsToAlloc)
          add(assertNotNull<std::bad_alloc>(std::malloc(bytes)), bytes);
          return mHead;
      }
  
      // enforce byte alignment of the T's
  #if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX14)
      static constexpr size_t ALIGNMENT =
          (std::max)(std::alignment_of<T>::value, std::alignment_of<T*>::value);
  #else
      static const size_t ALIGNMENT =
          (ROBIN_HOOD_STD::alignment_of<T>::value > ROBIN_HOOD_STD::alignment_of<T*>::value)
              ? ROBIN_HOOD_STD::alignment_of<T>::value
              : +ROBIN_HOOD_STD::alignment_of<T*>::value; // the + is for walkarround
  #endif
  
      static constexpr size_t ALIGNED_SIZE = ((sizeof(T) - 1) / ALIGNMENT + 1) * ALIGNMENT;
  
      static_assert(MinNumAllocs >= 1, "MinNumAllocs");
      static_assert(MaxNumAllocs >= MinNumAllocs, "MaxNumAllocs");
      static_assert(ALIGNED_SIZE >= sizeof(T*), "ALIGNED_SIZE");
      static_assert(0 == (ALIGNED_SIZE % sizeof(T*)), "ALIGNED_SIZE mod");
      static_assert(ALIGNMENT >= sizeof(T*), "ALIGNMENT");
  
      T* mHead{nullptr};
      T** mListForFree{nullptr};
  };
  
  template <typename T, size_t MinSize, size_t MaxSize, bool IsFlat>
  struct NodeAllocator;
  
  // dummy allocator that does nothing
  template <typename T, size_t MinSize, size_t MaxSize>
  struct NodeAllocator<T, MinSize, MaxSize, true> {
  
      // we are not using the data, so just free it.
      void addOrFree(void* ptr, size_t ROBIN_HOOD_UNUSED(numBytes) /*unused*/) noexcept {
          ROBIN_HOOD_LOG("std::free")
          std::free(ptr);
      }
  };
  
  template <typename T, size_t MinSize, size_t MaxSize>
  struct NodeAllocator<T, MinSize, MaxSize, false> : public BulkPoolAllocator<T, MinSize, MaxSize> {};
  
  // c++14 doesn't have is_nothrow_swappable, and clang++ 6.0.1 doesn't like it either, so I'm making
  // my own here.
  namespace swappable {
  #if ROBIN_HOOD(CXX) < ROBIN_HOOD(CXX17)
  using std::swap;
  template <typename T>
  struct nothrow {
      static const bool value = noexcept(swap(std::declval<T&>(), std::declval<T&>()));
  };
  #else
  template <typename T>
  struct nothrow {
      static const bool value = std::is_nothrow_swappable<T>::value;
  };
  #endif
  } // namespace swappable
  
  } // namespace detail
  
  struct is_transparent_tag {};
  
  // A custom pair implementation is used in the map because std::pair is not is_trivially_copyable,
  // which means it would  not be allowed to be used in std::memcpy. This struct is copyable, which is
  // also tested.
  template <typename T1, typename T2>
  struct pair {
      using first_type = T1;
      using second_type = T2;
  
      template <typename U1 = T1, typename U2 = T2,
                typename = typename std::enable_if<std::is_default_constructible<U1>::value &&
                                                   std::is_default_constructible<U2>::value>::type>
      constexpr pair() noexcept(noexcept(U1()) && noexcept(U2()))
          : first()
          , second() {}
  
      // pair constructors are explicit so we don't accidentally call this ctor when we don't have to.
      explicit constexpr pair(std::pair<T1, T2> const& o) noexcept(
          noexcept(T1(std::declval<T1 const&>())) && noexcept(T2(std::declval<T2 const&>())))
          : first(o.first)
          , second(o.second) {}
  
      // pair constructors are explicit so we don't accidentally call this ctor when we don't have to.
      explicit constexpr pair(std::pair<T1, T2>&& o) noexcept(noexcept(
          T1(std::move(std::declval<T1&&>()))) && noexcept(T2(std::move(std::declval<T2&&>()))))
          : first(std::move(o.first))
          , second(std::move(o.second)) {}
  
      constexpr pair(T1&& a, T2&& b) noexcept(noexcept(
          T1(std::move(std::declval<T1&&>()))) && noexcept(T2(std::move(std::declval<T2&&>()))))
          : first(std::move(a))
          , second(std::move(b)) {}
  
      template <typename U1, typename U2>
      constexpr pair(U1&& a, U2&& b) noexcept(noexcept(T1(std::forward<U1>(
          std::declval<U1&&>()))) && noexcept(T2(std::forward<U2>(std::declval<U2&&>()))))
          : first(std::forward<U1>(a))
          , second(std::forward<U2>(b)) {}
  
      template <typename... U1, typename... U2>
      // MSVC 2015 produces error "C2476: ‘constexpr’ constructor does not initialize all members"
      // if this constructor is constexpr
  #if !ROBIN_HOOD(BROKEN_CONSTEXPR)
      constexpr
  #endif
          pair(std::piecewise_construct_t /*unused*/, std::tuple<U1...> a,
               std::tuple<U2...>
                   b) noexcept(noexcept(pair(std::declval<std::tuple<U1...>&>(),
                                             std::declval<std::tuple<U2...>&>(),
                                             ROBIN_HOOD_STD::index_sequence_for<U1...>(),
                                             ROBIN_HOOD_STD::index_sequence_for<U2...>())))
          : pair(a, b, ROBIN_HOOD_STD::index_sequence_for<U1...>(),
                 ROBIN_HOOD_STD::index_sequence_for<U2...>()) {
      }
  
      // constructor called from the std::piecewise_construct_t ctor
      template <typename... U1, size_t... I1, typename... U2, size_t... I2>
      pair(std::tuple<U1...>& a, std::tuple<U2...>& b, ROBIN_HOOD_STD::index_sequence<I1...> /*unused*/, ROBIN_HOOD_STD::index_sequence<I2...> /*unused*/) noexcept(
          noexcept(T1(std::forward<U1>(std::get<I1>(
              std::declval<std::tuple<
                  U1...>&>()))...)) && noexcept(T2(std::
                                                       forward<U2>(std::get<I2>(
                                                           std::declval<std::tuple<U2...>&>()))...)))
          : first(std::forward<U1>(std::get<I1>(a))...)
          , second(std::forward<U2>(std::get<I2>(b))...) {
          // make visual studio compiler happy about warning about unused a & b.
          // Visual studio's pair implementation disables warning 4100.
          (void)a;
          (void)b;
      }
  
      void swap(pair<T1, T2>& o) noexcept((detail::swappable::nothrow<T1>::value) &&
                                          (detail::swappable::nothrow<T2>::value)) {
          using std::swap;
          swap(first, o.first);
          swap(second, o.second);
      }
  
      T1 first;  // NOLINT(misc-non-private-member-variables-in-classes)
      T2 second; // NOLINT(misc-non-private-member-variables-in-classes)
  };
  
  template <typename A, typename B>
  inline void swap(pair<A, B>& a, pair<A, B>& b) noexcept(
      noexcept(std::declval<pair<A, B>&>().swap(std::declval<pair<A, B>&>()))) {
      a.swap(b);
  }
  
  template <typename A, typename B>
  inline constexpr bool operator==(pair<A, B> const& x, pair<A, B> const& y) {
      return (x.first == y.first) && (x.second == y.second);
  }
  template <typename A, typename B>
  inline constexpr bool operator!=(pair<A, B> const& x, pair<A, B> const& y) {
      return !(x == y);
  }
  template <typename A, typename B>
  inline constexpr bool operator<(pair<A, B> const& x, pair<A, B> const& y) noexcept(noexcept(
      std::declval<A const&>() < std::declval<A const&>()) && noexcept(std::declval<B const&>() <
                                                                       std::declval<B const&>())) {
      return x.first < y.first || (!(y.first < x.first) && x.second < y.second);
  }
  template <typename A, typename B>
  inline constexpr bool operator>(pair<A, B> const& x, pair<A, B> const& y) {
      return y < x;
  }
  template <typename A, typename B>
  inline constexpr bool operator<=(pair<A, B> const& x, pair<A, B> const& y) {
      return !(x > y);
  }
  template <typename A, typename B>
  inline constexpr bool operator>=(pair<A, B> const& x, pair<A, B> const& y) {
      return !(x < y);
  }
  
  inline size_t hash_bytes(void const* ptr, size_t len) noexcept {
      static constexpr uint64_t m = UINT64_C(0xc6a4a7935bd1e995);
      static constexpr uint64_t seed = UINT64_C(0xe17a1465);
      static constexpr unsigned int r = 47;
  
      auto const* const data64 = static_cast<uint64_t const*>(ptr);
      uint64_t h = seed ^ (len * m);
  
      size_t const n_blocks = len / 8;
      for (size_t i = 0; i < n_blocks; ++i) {
          auto k = detail::unaligned_load<uint64_t>(data64 + i);
  
          k *= m;
          k ^= k >> r;
          k *= m;
  
          h ^= k;
          h *= m;
      }
  
      auto const* const data8 = reinterpret_cast<uint8_t const*>(data64 + n_blocks);
      switch (len & 7U) {
      case 7:
          h ^= static_cast<uint64_t>(data8[6]) << 48U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 6:
          h ^= static_cast<uint64_t>(data8[5]) << 40U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 5:
          h ^= static_cast<uint64_t>(data8[4]) << 32U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 4:
          h ^= static_cast<uint64_t>(data8[3]) << 24U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 3:
          h ^= static_cast<uint64_t>(data8[2]) << 16U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 2:
          h ^= static_cast<uint64_t>(data8[1]) << 8U;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      case 1:
          h ^= static_cast<uint64_t>(data8[0]);
          h *= m;
          ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
      default:
          break;
      }
  
      h ^= h >> r;
  
      // not doing the final step here, because this will be done by keyToIdx anyways
      // h *= m;
      // h ^= h >> r;
      return static_cast<size_t>(h);
  }
  
  inline size_t hash_int(uint64_t x) noexcept {
      // tried lots of different hashes, let's stick with murmurhash3. It's simple, fast, well tested,
      // and doesn't need any special 128bit operations.
      x ^= x >> 33U;
      x *= UINT64_C(0xff51afd7ed558ccd);
      x ^= x >> 33U;
  
      // not doing the final step here, because this will be done by keyToIdx anyways
      // x *= UINT64_C(0xc4ceb9fe1a85ec53);
      // x ^= x >> 33U;
      return static_cast<size_t>(x);
  }
  
  // A thin wrapper around std::hash, performing an additional simple mixing step of the result.
  template <typename T, typename Enable = void>
  struct hash : public std::hash<T> {
      size_t operator()(T const& obj) const
          noexcept(noexcept(std::declval<std::hash<T>>().operator()(std::declval<T const&>()))) {
          // call base hash
          auto result = std::hash<T>::operator()(obj);
          // return mixed of that, to be save against identity has
          return hash_int(static_cast<detail::SizeT>(result));
      }
  };
  
  template <typename CharT>
  struct hash<std::basic_string<CharT>> {
      size_t operator()(std::basic_string<CharT> const& str) const noexcept {
          return hash_bytes(str.data(), sizeof(CharT) * str.size());
      }
  };
  
  #if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX17)
  template <typename CharT>
  struct hash<std::basic_string_view<CharT>> {
      size_t operator()(std::basic_string_view<CharT> const& sv) const noexcept {
          return hash_bytes(sv.data(), sizeof(CharT) * sv.size());
      }
  };
  #endif
  
  template <class T>
  struct hash<T*> {
      size_t operator()(T* ptr) const noexcept {
          return hash_int(reinterpret_cast<detail::SizeT>(ptr));
      }
  };
  
  template <class T>
  struct hash<std::unique_ptr<T>> {
      size_t operator()(std::unique_ptr<T> const& ptr) const noexcept {
          return hash_int(reinterpret_cast<detail::SizeT>(ptr.get()));
      }
  };
  
  template <class T>
  struct hash<std::shared_ptr<T>> {
      size_t operator()(std::shared_ptr<T> const& ptr) const noexcept {
          return hash_int(reinterpret_cast<detail::SizeT>(ptr.get()));
      }
  };
  
  template <typename Enum>
  struct hash<Enum, typename std::enable_if<std::is_enum<Enum>::value>::type> {
      size_t operator()(Enum e) const noexcept {
          using Underlying = typename std::underlying_type<Enum>::type;
          return hash<Underlying>{}(static_cast<Underlying>(e));
      }
  };
  
  #define ROBIN_HOOD_HASH_INT(T)                           \
      template <>                                          \
      struct hash<T> {                                     \
          size_t operator()(T const& obj) const noexcept { \
              return hash_int(static_cast<uint64_t>(obj)); \
          }                                                \
      }
  
  #if defined(__GNUC__) && !defined(__clang__)
  #    pragma GCC diagnostic push
  #    pragma GCC diagnostic ignored "-Wuseless-cast"
  #endif
  // see https://en.cppreference.com/w/cpp/utility/hash
  ROBIN_HOOD_HASH_INT(bool);
  ROBIN_HOOD_HASH_INT(char);
  ROBIN_HOOD_HASH_INT(signed char);
  ROBIN_HOOD_HASH_INT(unsigned char);
  ROBIN_HOOD_HASH_INT(char16_t);
  ROBIN_HOOD_HASH_INT(char32_t);
  #if ROBIN_HOOD(HAS_NATIVE_WCHART)
  ROBIN_HOOD_HASH_INT(wchar_t);
  #endif
  ROBIN_HOOD_HASH_INT(short);
  ROBIN_HOOD_HASH_INT(unsigned short);
  ROBIN_HOOD_HASH_INT(int);
  ROBIN_HOOD_HASH_INT(unsigned int);
  ROBIN_HOOD_HASH_INT(long);
  ROBIN_HOOD_HASH_INT(long long);
  ROBIN_HOOD_HASH_INT(unsigned long);
  ROBIN_HOOD_HASH_INT(unsigned long long);
  #if defined(__GNUC__) && !defined(__clang__)
  #    pragma GCC diagnostic pop
  #endif
  namespace detail {
  
  template <typename T>
  struct void_type {
      using type = void;
  };
  
  template <typename T, typename = void>
  struct has_is_transparent : public std::false_type {};
  
  template <typename T>
  struct has_is_transparent<T, typename void_type<typename T::is_transparent>::type>
      : public std::true_type {};
  
  // using wrapper classes for hash and key_equal prevents the diamond problem when the same type
  // is used. see https://stackoverflow.com/a/28771920/48181
  template <typename T>
  struct WrapHash : public T {
      WrapHash() = default;
      explicit WrapHash(T const& o) noexcept(noexcept(T(std::declval<T const&>())))
          : T(o) {}
  };
  
  template <typename T>
  struct WrapKeyEqual : public T {
      WrapKeyEqual() = default;
      explicit WrapKeyEqual(T const& o) noexcept(noexcept(T(std::declval<T const&>())))
          : T(o) {}
  };
  
  // A highly optimized hashmap implementation, using the Robin Hood algorithm.
  //
  // In most cases, this map should be usable as a drop-in replacement for std::unordered_map, but
  // be about 2x faster in most cases and require much less allocations.
  //
  // This implementation uses the following memory layout:
  //
  // [Node, Node, ... Node | info, info, ... infoSentinel ]
  //
  // * Node: either a DataNode that directly has the std::pair<key, val> as member,
  //   or a DataNode with a pointer to std::pair<key,val>. Which DataNode representation to use
  //   depends on how fast the swap() operation is. Heuristically, this is automatically choosen
  //   based on sizeof(). there are always 2^n Nodes.
  //
  // * info: Each Node in the map has a corresponding info byte, so there are 2^n info bytes.
  //   Each byte is initialized to 0, meaning the corresponding Node is empty. Set to 1 means the
  //   corresponding node contains data. Set to 2 means the corresponding Node is filled, but it
  //   actually belongs to the previous position and was pushed out because that place is already
  //   taken.
  //
  // * infoSentinel: Sentinel byte set to 1, so that iterator's ++ can stop at end() without the
  //   need for a idx variable.
  //
  // According to STL, order of templates has effect on throughput. That's why I've moved the
  // boolean to the front.
  // https://www.reddit.com/r/cpp/comments/ahp6iu/compile_time_binary_size_reductions_and_cs_future/eeguck4/
  template <bool IsFlat, size_t MaxLoadFactor100, typename Key, typename T, typename Hash,
            typename KeyEqual>
  class Table
      : public WrapHash<Hash>,
        public WrapKeyEqual<KeyEqual>,
        detail::NodeAllocator<
            typename std::conditional<
                std::is_void<T>::value, Key,
                robin_hood::pair<typename std::conditional<IsFlat, Key, Key const>::type, T>>::type,
            4, 16384, IsFlat> {
  public:
      static constexpr bool is_flat = IsFlat;
      static constexpr bool is_map = !std::is_void<T>::value;
      static constexpr bool is_set = !is_map;
      static constexpr bool is_transparent =
          has_is_transparent<Hash>::value && has_is_transparent<KeyEqual>::value;
  
      using key_type = Key;
      using mapped_type = T;
      using value_type = typename std::conditional<
          is_set, Key,
          robin_hood::pair<typename std::conditional<is_flat, Key, Key const>::type, T>>::type;
      using size_type = size_t;
      using hasher = Hash;
      using key_equal = KeyEqual;
      using Self = Table<IsFlat, MaxLoadFactor100, key_type, mapped_type, hasher, key_equal>;
  
  private:
      static_assert(MaxLoadFactor100 > 10 && MaxLoadFactor100 < 100,
                    "MaxLoadFactor100 needs to be >10 && < 100");
  
      using WHash = WrapHash<Hash>;
      using WKeyEqual = WrapKeyEqual<KeyEqual>;
  
      // configuration defaults
  
      // make sure we have 8 elements, needed to quickly rehash mInfo
      static constexpr size_t InitialNumElements = sizeof(uint64_t);
      static constexpr uint32_t InitialInfoNumBits = 5;
      static constexpr uint8_t InitialInfoInc = 1U << InitialInfoNumBits;
      static constexpr size_t InfoMask = InitialInfoInc - 1U;
      static constexpr uint8_t InitialInfoHashShift = 0;
      using DataPool = detail::NodeAllocator<value_type, 4, 16384, IsFlat>;
  
      // type needs to be wider than uint8_t.
      using InfoType = uint32_t;
  
      // DataNode ////////////////////////////////////////////////////////
  
      // Primary template for the data node. We have special implementations for small and big
      // objects. For large objects it is assumed that swap() is fairly slow, so we allocate these
      // on the heap so swap merely swaps a pointer.
      template <typename M, bool>
      class DataNode {};
  
      // Small: just allocate on the stack.
      template <typename M>
      class DataNode<M, true> final {
      public:
          template <typename... Args>
          explicit DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, Args&&... args) noexcept(
              noexcept(value_type(std::forward<Args>(args)...)))
              : mData(std::forward<Args>(args)...) {}
  
          DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, DataNode<M, true>&& n) noexcept(
              std::is_nothrow_move_constructible<value_type>::value)
              : mData(std::move(n.mData)) {}
  
          // doesn't do anything
          void destroy(M& ROBIN_HOOD_UNUSED(map) /*unused*/) noexcept {}
          void destroyDoNotDeallocate() noexcept {}
  
          value_type const* operator->() const noexcept {
              return &mData;
          }
          value_type* operator->() noexcept {
              return &mData;
          }
  
          const value_type& operator*() const noexcept {
              return mData;
          }
  
          value_type& operator*() noexcept {
              return mData;
          }
  
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, typename VT::first_type&>::type getFirst() noexcept {
              return mData.first;
          }
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_set, VT&>::type getFirst() noexcept {
              return mData;
          }
  
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, typename VT::first_type const&>::type
              getFirst() const noexcept {
              return mData.first;
          }
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_set, VT const&>::type getFirst() const noexcept {
              return mData;
          }
  
          template <typename MT = mapped_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, MT&>::type getSecond() noexcept {
              return mData.second;
          }
  
          template <typename MT = mapped_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_set, MT const&>::type getSecond() const noexcept {
              return mData.second;
          }
  
          void swap(DataNode<M, true>& o) noexcept(
              noexcept(std::declval<value_type>().swap(std::declval<value_type>()))) {
              mData.swap(o.mData);
          }
  
      private:
          value_type mData;
      };
  
      // big object: allocate on heap.
      template <typename M>
      class DataNode<M, false> {
      public:
          template <typename... Args>
          explicit DataNode(M& map, Args&&... args)
              : mData(map.allocate()) {
              ::new (static_cast<void*>(mData)) value_type(std::forward<Args>(args)...);
          }
  
          DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, DataNode<M, false>&& n) noexcept
              : mData(std::move(n.mData)) {}
  
          void destroy(M& map) noexcept {
              // don't deallocate, just put it into list of datapool.
              mData->~value_type();
              map.deallocate(mData);
          }
  
          void destroyDoNotDeallocate() noexcept {
              mData->~value_type();
          }
  
          value_type const* operator->() const noexcept {
              return mData;
          }
  
          value_type* operator->() noexcept {
              return mData;
          }
  
          const value_type& operator*() const {
              return *mData;
          }
  
          value_type& operator*() {
              return *mData;
          }
  
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, typename VT::first_type&>::type getFirst() noexcept {
              return mData->first;
          }
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_set, VT&>::type getFirst() noexcept {
              return *mData;
          }
  
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, typename VT::first_type const&>::type
              getFirst() const noexcept {
              return mData->first;
          }
          template <typename VT = value_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_set, VT const&>::type getFirst() const noexcept {
              return *mData;
          }
  
          template <typename MT = mapped_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, MT&>::type getSecond() noexcept {
              return mData->second;
          }
  
          template <typename MT = mapped_type>
          ROBIN_HOOD(NODISCARD)
          typename std::enable_if<is_map, MT const&>::type getSecond() const noexcept {
              return mData->second;
          }
  
          void swap(DataNode<M, false>& o) noexcept {
              using std::swap;
              swap(mData, o.mData);
          }
  
      private:
          value_type* mData;
      };
  
      using Node = DataNode<Self, IsFlat>;
  
      // helpers for insertKeyPrepareEmptySpot: extract first entry (only const required)
      ROBIN_HOOD(NODISCARD) key_type const& getFirstConst(Node const& n) const noexcept {
          return n.getFirst();
      }
  
      // in case we have void mapped_type, we are not using a pair, thus we just route k through.
      // No need to disable this because it's just not used if not applicable.
      ROBIN_HOOD(NODISCARD) key_type const& getFirstConst(key_type const& k) const noexcept {
          return k;
      }
  
      // in case we have non-void mapped_type, we have a standard robin_hood::pair
      template <typename Q = mapped_type>
      ROBIN_HOOD(NODISCARD)
      typename std::enable_if<!std::is_void<Q>::value, key_type const&>::type
          getFirstConst(value_type const& vt) const noexcept {
          return vt.first;
      }
  
      // Cloner //////////////////////////////////////////////////////////
  
      template <typename M, bool UseMemcpy>
      struct Cloner;
  
      // fast path: Just copy data, without allocating anything.
      template <typename M>
      struct Cloner<M, true> {
          void operator()(M const& source, M& target) const {
              auto const* const src = reinterpret_cast<char const*>(source.mKeyVals);
              auto* tgt = reinterpret_cast<char*>(target.mKeyVals);
              auto const numElementsWithBuffer = target.calcNumElementsWithBuffer(target.mMask + 1);
              std::copy(src, src + target.calcNumBytesTotal(numElementsWithBuffer), tgt);
          }
      };
  
      template <typename M>
      struct Cloner<M, false> {
          void operator()(M const& s, M& t) const {
              auto const numElementsWithBuffer = t.calcNumElementsWithBuffer(t.mMask + 1);
              std::copy(s.mInfo, s.mInfo + t.calcNumBytesInfo(numElementsWithBuffer), t.mInfo);
  
              for (size_t i = 0; i < numElementsWithBuffer; ++i) {
                  if (t.mInfo[i]) {
                      ::new (static_cast<void*>(t.mKeyVals + i)) Node(t, *s.mKeyVals[i]);
                  }
              }
          }
      };
  
      // Destroyer ///////////////////////////////////////////////////////
  
      template <typename M, bool IsFlatAndTrivial>
      struct Destroyer {};
  
      template <typename M>
      struct Destroyer<M, true> {
          void nodes(M& m) const noexcept {
              m.mNumElements = 0;
          }
  
          void nodesDoNotDeallocate(M& m) const noexcept {
              m.mNumElements = 0;
          }
      };
  
      template <typename M>
      struct Destroyer<M, false> {
          void nodes(M& m) const noexcept {
              m.mNumElements = 0;
              // clear also resets mInfo to 0, that's sometimes not necessary.
              auto const numElementsWithBuffer = m.calcNumElementsWithBuffer(m.mMask + 1);
  
              for (size_t idx = 0; idx < numElementsWithBuffer; ++idx) {
                  if (0 != m.mInfo[idx]) {
                      Node& n = m.mKeyVals[idx];
                      n.destroy(m);
                      n.~Node();
                  }
              }
          }
  
          void nodesDoNotDeallocate(M& m) const noexcept {
              m.mNumElements = 0;
              // clear also resets mInfo to 0, that's sometimes not necessary.
              auto const numElementsWithBuffer = m.calcNumElementsWithBuffer(m.mMask + 1);
              for (size_t idx = 0; idx < numElementsWithBuffer; ++idx) {
                  if (0 != m.mInfo[idx]) {
                      Node& n = m.mKeyVals[idx];
                      n.destroyDoNotDeallocate();
                      n.~Node();
                  }
              }
          }
      };
  
      // Iter ////////////////////////////////////////////////////////////
  
      struct fast_forward_tag {};
  
      // generic iterator for both const_iterator and iterator.
      template <bool IsConst>
      // NOLINTNEXTLINE(hicpp-special-member-functions,cppcoreguidelines-special-member-functions)
      class Iter {
      private:
          using NodePtr = typename std::conditional<IsConst, Node const*, Node*>::type;
  
      public:
          using difference_type = std::ptrdiff_t;
          using value_type = typename Self::value_type;
          using reference = typename std::conditional<IsConst, value_type const&, value_type&>::type;
          using pointer = typename std::conditional<IsConst, value_type const*, value_type*>::type;
          using iterator_category = std::forward_iterator_tag;
  
          // default constructed iterator can be compared to itself, but WON'T return true when
          // compared to end().
          Iter() = default;
  
          // Rule of zero: nothing specified. The conversion constructor is only enabled for
          // iterator to const_iterator, so it doesn't accidentally work as a copy ctor.
  
          // Conversion constructor from iterator to const_iterator.
          template <bool OtherIsConst,
                    typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
          // NOLINTNEXTLINE(hicpp-explicit-conversions)
          Iter(Iter<OtherIsConst> const& other) noexcept
              : mKeyVals(other.mKeyVals)
              , mInfo(other.mInfo) {}
  
          Iter(NodePtr valPtr, uint8_t const* infoPtr) noexcept
              : mKeyVals(valPtr)
              , mInfo(infoPtr) {}
  
          Iter(NodePtr valPtr, uint8_t const* infoPtr,
               fast_forward_tag ROBIN_HOOD_UNUSED(tag) /*unused*/) noexcept
              : mKeyVals(valPtr)
              , mInfo(infoPtr) {
              fastForward();
          }
  
          template <bool OtherIsConst,
                    typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
          Iter& operator=(Iter<OtherIsConst> const& other) noexcept {
              mKeyVals = other.mKeyVals;
              mInfo = other.mInfo;
              return *this;
          }
  
          // prefix increment. Undefined behavior if we are at end()!
          Iter& operator++() noexcept {
              mInfo++;
              mKeyVals++;
              fastForward();
              return *this;
          }
  
          Iter operator++(int) noexcept {
              Iter tmp = *this;
              ++(*this);
              return tmp;
          }
  
          reference operator*() const {
              return **mKeyVals;
          }
  
          pointer operator->() const {
              return &**mKeyVals;
          }
  
          template <bool O>
          bool operator==(Iter<O> const& o) const noexcept {
              return mKeyVals == o.mKeyVals;
          }
  
          template <bool O>
          bool operator!=(Iter<O> const& o) const noexcept {
              return mKeyVals != o.mKeyVals;
          }
  
      private:
          // fast forward to the next non-free info byte
          // I've tried a few variants that don't depend on intrinsics, but unfortunately they are
          // quite a bit slower than this one. So I've reverted that change again. See map_benchmark.
          void fastForward() noexcept {
              size_t n = 0;
              while (0U == (n = detail::unaligned_load<size_t>(mInfo))) {
                  mInfo += sizeof(size_t);
                  mKeyVals += sizeof(size_t);
              }
  #if defined(ROBIN_HOOD_DISABLE_INTRINSICS)
              // we know for certain that within the next 8 bytes we'll find a non-zero one.
              if (ROBIN_HOOD_UNLIKELY(0U == detail::unaligned_load<uint32_t>(mInfo))) {
                  mInfo += 4;
                  mKeyVals += 4;
              }
              if (ROBIN_HOOD_UNLIKELY(0U == detail::unaligned_load<uint16_t>(mInfo))) {
                  mInfo += 2;
                  mKeyVals += 2;
              }
              if (ROBIN_HOOD_UNLIKELY(0U == *mInfo)) {
                  mInfo += 1;
                  mKeyVals += 1;
              }
  #else
  #    if ROBIN_HOOD(LITTLE_ENDIAN)
              auto inc = ROBIN_HOOD_COUNT_TRAILING_ZEROES(n) / 8;
  #    else
              auto inc = ROBIN_HOOD_COUNT_LEADING_ZEROES(n) / 8;
  #    endif
              mInfo += inc;
              mKeyVals += inc;
  #endif
          }
  
          friend class Table<IsFlat, MaxLoadFactor100, key_type, mapped_type, hasher, key_equal>;
          NodePtr mKeyVals{nullptr};
          uint8_t const* mInfo{nullptr};
      };
  
      ////////////////////////////////////////////////////////////////////
  
      // highly performance relevant code.
      // Lower bits are used for indexing into the array (2^n size)
      // The upper 1-5 bits need to be a reasonable good hash, to save comparisons.
      template <typename HashKey>
      void keyToIdx(HashKey&& key, size_t* idx, InfoType* info) const {
          // In addition to whatever hash is used, add another mul & shift so we get better hashing.
          // This serves as a bad hash prevention, if the given data is
          // badly mixed.
          auto h = static_cast<uint64_t>(WHash::operator()(key));
  
          h *= mHashMultiplier;
          h ^= h >> 33U;
  
          // the lower InitialInfoNumBits are reserved for info.
          *info = mInfoInc + static_cast<InfoType>((h & InfoMask) >> mInfoHashShift);
          *idx = (static_cast<size_t>(h) >> InitialInfoNumBits) & mMask;
      }
  
      // forwards the index by one, wrapping around at the end
      void next(InfoType* info, size_t* idx) const noexcept {
          *idx = *idx + 1;
          *info += mInfoInc;
      }
  
      void nextWhileLess(InfoType* info, size_t* idx) const noexcept {
          // unrolling this by hand did not bring any speedups.
          while (*info < mInfo[*idx]) {
              next(info, idx);
          }
      }
  
      // Shift everything up by one element. Tries to move stuff around.
      void
      shiftUp(size_t startIdx,
              size_t const insertion_idx) noexcept(std::is_nothrow_move_assignable<Node>::value) {
          auto idx = startIdx;
          ::new (static_cast<void*>(mKeyVals + idx)) Node(std::move(mKeyVals[idx - 1]));
          while (--idx != insertion_idx) {
              mKeyVals[idx] = std::move(mKeyVals[idx - 1]);
          }
  
          idx = startIdx;
          while (idx != insertion_idx) {
              ROBIN_HOOD_COUNT(shiftUp)
              mInfo[idx] = static_cast<uint8_t>(mInfo[idx - 1] + mInfoInc);
              if (ROBIN_HOOD_UNLIKELY(mInfo[idx] + mInfoInc > 0xFF)) {
                  mMaxNumElementsAllowed = 0;
              }
              --idx;
          }
      }
  
      void shiftDown(size_t idx) noexcept(std::is_nothrow_move_assignable<Node>::value) {
          // until we find one that is either empty or has zero offset.
          // TODO(martinus) we don't need to move everything, just the last one for the same
          // bucket.
          mKeyVals[idx].destroy(*this);
  
          // until we find one that is either empty or has zero offset.
          while (mInfo[idx + 1] >= 2 * mInfoInc) {
              ROBIN_HOOD_COUNT(shiftDown)
              mInfo[idx] = static_cast<uint8_t>(mInfo[idx + 1] - mInfoInc);
              mKeyVals[idx] = std::move(mKeyVals[idx + 1]);
              ++idx;
          }
  
          mInfo[idx] = 0;
          // don't destroy, we've moved it
          // mKeyVals[idx].destroy(*this);
          mKeyVals[idx].~Node();
      }
  
      // copy of find(), except that it returns iterator instead of const_iterator.
      template <typename Other>
      ROBIN_HOOD(NODISCARD)
      size_t findIdx(Other const& key) const {
          size_t idx{};
          InfoType info{};
          keyToIdx(key, &idx, &info);
  
          do {
              // unrolling this twice gives a bit of a speedup. More unrolling did not help.
              if (info == mInfo[idx] &&
                  ROBIN_HOOD_LIKELY(WKeyEqual::operator()(key, mKeyVals[idx].getFirst()))) {
                  return idx;
              }
              next(&info, &idx);
              if (info == mInfo[idx] &&
                  ROBIN_HOOD_LIKELY(WKeyEqual::operator()(key, mKeyVals[idx].getFirst()))) {
                  return idx;
              }
              next(&info, &idx);
          } while (info <= mInfo[idx]);
  
          // nothing found!
          return mMask == 0 ? 0
                            : static_cast<size_t>(std::distance(
                                  mKeyVals, reinterpret_cast_no_cast_align_warning<Node*>(mInfo)));
      }
  
      void cloneData(const Table& o) {
          Cloner<Table, IsFlat && ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(Node)>()(o, *this);
      }
  
      // inserts a keyval that is guaranteed to be new, e.g. when the hashmap is resized.
      // @return True on success, false if something went wrong
      void insert_move(Node&& keyval) {
          // we don't retry, fail if overflowing
          // don't need to check max num elements
          if (0 == mMaxNumElementsAllowed && !try_increase_info()) {
              throwOverflowError();
          }
  
          size_t idx{};
          InfoType info{};
          keyToIdx(keyval.getFirst(), &idx, &info);
  
          // skip forward. Use <= because we are certain that the element is not there.
          while (info <= mInfo[idx]) {
              idx = idx + 1;
              info += mInfoInc;
          }
  
          // key not found, so we are now exactly where we want to insert it.
          auto const insertion_idx = idx;
          auto const insertion_info = static_cast<uint8_t>(info);
          if (ROBIN_HOOD_UNLIKELY(insertion_info + mInfoInc > 0xFF)) {
              mMaxNumElementsAllowed = 0;
          }
  
          // find an empty spot
          while (0 != mInfo[idx]) {
              next(&info, &idx);
          }
  
          auto& l = mKeyVals[insertion_idx];
          if (idx == insertion_idx) {
              ::new (static_cast<void*>(&l)) Node(std::move(keyval));
          } else {
              shiftUp(idx, insertion_idx);
              l = std::move(keyval);
          }
  
          // put at empty spot
          mInfo[insertion_idx] = insertion_info;
  
          ++mNumElements;
      }
  
  public:
      using iterator = Iter<false>;
      using const_iterator = Iter<true>;
  
      Table() noexcept(noexcept(Hash()) && noexcept(KeyEqual()))
          : WHash()
          , WKeyEqual() {
          ROBIN_HOOD_TRACE(this)
      }
  
      // Creates an empty hash map. Nothing is allocated yet, this happens at the first insert.
      // This tremendously speeds up ctor & dtor of a map that never receives an element. The
      // penalty is payed at the first insert, and not before. Lookup of this empty map works
      // because everybody points to DummyInfoByte::b. parameter bucket_count is dictated by the
      // standard, but we can ignore it.
      explicit Table(
          size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/, const Hash& h = Hash{},
          const KeyEqual& equal = KeyEqual{}) noexcept(noexcept(Hash(h)) && noexcept(KeyEqual(equal)))
          : WHash(h)
          , WKeyEqual(equal) {
          ROBIN_HOOD_TRACE(this)
      }
  
      template <typename Iter>
      Table(Iter first, Iter last, size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/ = 0,
            const Hash& h = Hash{}, const KeyEqual& equal = KeyEqual{})
          : WHash(h)
          , WKeyEqual(equal) {
          ROBIN_HOOD_TRACE(this)
          insert(first, last);
      }
  
      Table(std::initializer_list<value_type> initlist,
            size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/ = 0, const Hash& h = Hash{},
            const KeyEqual& equal = KeyEqual{})
          : WHash(h)
          , WKeyEqual(equal) {
          ROBIN_HOOD_TRACE(this)
          insert(initlist.begin(), initlist.end());
      }
  
      Table(Table&& o) noexcept
          : WHash(std::move(static_cast<WHash&>(o)))
          , WKeyEqual(std::move(static_cast<WKeyEqual&>(o)))
          , DataPool(std::move(static_cast<DataPool&>(o))) {
          ROBIN_HOOD_TRACE(this)
          if (o.mMask) {
              mHashMultiplier = std::move(o.mHashMultiplier);
              mKeyVals = std::move(o.mKeyVals);
              mInfo = std::move(o.mInfo);
              mNumElements = std::move(o.mNumElements);
              mMask = std::move(o.mMask);
              mMaxNumElementsAllowed = std::move(o.mMaxNumElementsAllowed);
              mInfoInc = std::move(o.mInfoInc);
              mInfoHashShift = std::move(o.mInfoHashShift);
              // set other's mask to 0 so its destructor won't do anything
              o.init();
          }
      }
  
      Table& operator=(Table&& o) noexcept {
          ROBIN_HOOD_TRACE(this)
          if (&o != this) {
              if (o.mMask) {
                  // only move stuff if the other map actually has some data
                  destroy();
                  mHashMultiplier = std::move(o.mHashMultiplier);
                  mKeyVals = std::move(o.mKeyVals);
                  mInfo = std::move(o.mInfo);
                  mNumElements = std::move(o.mNumElements);
                  mMask = std::move(o.mMask);
                  mMaxNumElementsAllowed = std::move(o.mMaxNumElementsAllowed);
                  mInfoInc = std::move(o.mInfoInc);
                  mInfoHashShift = std::move(o.mInfoHashShift);
                  WHash::operator=(std::move(static_cast<WHash&>(o)));
                  WKeyEqual::operator=(std::move(static_cast<WKeyEqual&>(o)));
                  DataPool::operator=(std::move(static_cast<DataPool&>(o)));
  
                  o.init();
  
              } else {
                  // nothing in the other map => just clear us.
                  clear();
              }
          }
          return *this;
      }
  
      Table(const Table& o)
          : WHash(static_cast<const WHash&>(o))
          , WKeyEqual(static_cast<const WKeyEqual&>(o))
          , DataPool(static_cast<const DataPool&>(o)) {
          ROBIN_HOOD_TRACE(this)
          if (!o.empty()) {
              // not empty: create an exact copy. it is also possible to just iterate through all
              // elements and insert them, but copying is probably faster.
  
              auto const numElementsWithBuffer = calcNumElementsWithBuffer(o.mMask + 1);
              auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);
  
              ROBIN_HOOD_LOG("std::malloc " << numBytesTotal << " = calcNumBytesTotal("
                                            << numElementsWithBuffer << ")")
              mHashMultiplier = o.mHashMultiplier;
              mKeyVals = static_cast<Node*>(
                  detail::assertNotNull<std::bad_alloc>(std::malloc(numBytesTotal)));
              // no need for calloc because clonData does memcpy
              mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);
              mNumElements = o.mNumElements;
              mMask = o.mMask;
              mMaxNumElementsAllowed = o.mMaxNumElementsAllowed;
              mInfoInc = o.mInfoInc;
              mInfoHashShift = o.mInfoHashShift;
              cloneData(o);
          }
      }
  
      // Creates a copy of the given map. Copy constructor of each entry is used.
      // Not sure why clang-tidy thinks this doesn't handle self assignment, it does
      // NOLINTNEXTLINE(bugprone-unhandled-self-assignment,cert-oop54-cpp)
      Table& operator=(Table const& o) {
          ROBIN_HOOD_TRACE(this)
          if (&o == this) {
              // prevent assigning of itself
              return *this;
          }
  
          // we keep using the old allocator and not assign the new one, because we want to keep
          // the memory available. when it is the same size.
          if (o.empty()) {
              if (0 == mMask) {
                  // nothing to do, we are empty too
                  return *this;
              }
  
              // not empty: destroy what we have there
              // clear also resets mInfo to 0, that's sometimes not necessary.
              destroy();
              init();
              WHash::operator=(static_cast<const WHash&>(o));
              WKeyEqual::operator=(static_cast<const WKeyEqual&>(o));
              DataPool::operator=(static_cast<DataPool const&>(o));
  
              return *this;
          }
  
          // clean up old stuff
          Destroyer<Self, IsFlat && std::is_trivially_destructible<Node>::value>{}.nodes(*this);
  
          if (mMask != o.mMask) {
              // no luck: we don't have the same array size allocated, so we need to realloc.
              if (0 != mMask) {
                  // only deallocate if we actually have data!
                  ROBIN_HOOD_LOG("std::free")
                  std::free(mKeyVals);
              }
  
              auto const numElementsWithBuffer = calcNumElementsWithBuffer(o.mMask + 1);
              auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);
              ROBIN_HOOD_LOG("std::malloc " << numBytesTotal << " = calcNumBytesTotal("
                                            << numElementsWithBuffer << ")")
              mKeyVals = static_cast<Node*>(
                  detail::assertNotNull<std::bad_alloc>(std::malloc(numBytesTotal)));
  
              // no need for calloc here because cloneData performs a memcpy.
              mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);
              // sentinel is set in cloneData
          }
          WHash::operator=(static_cast<const WHash&>(o));
          WKeyEqual::operator=(static_cast<const WKeyEqual&>(o));
          DataPool::operator=(static_cast<DataPool const&>(o));
          mHashMultiplier = o.mHashMultiplier;
          mNumElements = o.mNumElements;
          mMask = o.mMask;
          mMaxNumElementsAllowed = o.mMaxNumElementsAllowed;
          mInfoInc = o.mInfoInc;
          mInfoHashShift = o.mInfoHashShift;
          cloneData(o);
  
          return *this;
      }
  
      // Swaps everything between the two maps.
      void swap(Table& o) {
          ROBIN_HOOD_TRACE(this)
          using std::swap;
          swap(o, *this);
      }
  
      // Clears all data, without resizing.
      void clear() {
          ROBIN_HOOD_TRACE(this)
          if (empty()) {
              // don't do anything! also important because we don't want to write to
              // DummyInfoByte::b, even though we would just write 0 to it.
              return;
          }
  
          Destroyer<Self, IsFlat && std::is_trivially_destructible<Node>::value>{}.nodes(*this);
  
          auto const numElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);
          // clear everything, then set the sentinel again
          uint8_t const z = 0;
          std::fill(mInfo, mInfo + calcNumBytesInfo(numElementsWithBuffer), z);
          mInfo[numElementsWithBuffer] = 1;
  
          mInfoInc = InitialInfoInc;
          mInfoHashShift = InitialInfoHashShift;
      }
  
      // Destroys the map and all it's contents.
      ~Table() {
          ROBIN_HOOD_TRACE(this)
          destroy();
      }
  
      // Checks if both tables contain the same entries. Order is irrelevant.
      bool operator==(const Table& other) const {
          ROBIN_HOOD_TRACE(this)
          if (other.size() != size()) {
              return false;
          }
          for (auto const& otherEntry : other) {
              if (!has(otherEntry)) {
                  return false;
              }
          }
  
          return true;
      }
  
      bool operator!=(const Table& other) const {
          ROBIN_HOOD_TRACE(this)
          return !operator==(other);
      }
  
      template <typename Q = mapped_type>
      typename std::enable_if<!std::is_void<Q>::value, Q&>::type operator[](const key_type& key) {
          ROBIN_HOOD_TRACE(this)
          auto idxAndState = insertKeyPrepareEmptySpot(key);
          switch (idxAndState.second) {
          case InsertionState::key_found:
              break;
  
          case InsertionState::new_node:
              ::new (static_cast<void*>(&mKeyVals[idxAndState.first]))
                  Node(*this, std::piecewise_construct, std::forward_as_tuple(key),
                       std::forward_as_tuple());
              break;
  
          case InsertionState::overwrite_node:
              mKeyVals[idxAndState.first] = Node(*this, std::piecewise_construct,
                                                 std::forward_as_tuple(key), std::forward_as_tuple());
              break;
  
          case InsertionState::overflow_error:
              throwOverflowError();
          }
  
          return mKeyVals[idxAndState.first].getSecond();
      }
  
      template <typename Q = mapped_type>
      typename std::enable_if<!std::is_void<Q>::value, Q&>::type operator[](key_type&& key) {
          ROBIN_HOOD_TRACE(this)
          auto idxAndState = insertKeyPrepareEmptySpot(key);
          switch (idxAndState.second) {
          case InsertionState::key_found:
              break;
  
          case InsertionState::new_node:
              ::new (static_cast<void*>(&mKeyVals[idxAndState.first]))
                  Node(*this, std::piecewise_construct, std::forward_as_tuple(std::move(key)),
                       std::forward_as_tuple());
              break;
  
          case InsertionState::overwrite_node:
              mKeyVals[idxAndState.first] =
                  Node(*this, std::piecewise_construct, std::forward_as_tuple(std::move(key)),
                       std::forward_as_tuple());
              break;
  
          case InsertionState::overflow_error:
              throwOverflowError();
          }
  
          return mKeyVals[idxAndState.first].getSecond();
      }
  
      template <typename Iter>
      void insert(Iter first, Iter last) {
          for (; first != last; ++first) {
              // value_type ctor needed because this might be called with std::pair's
              insert(value_type(*first));
          }
      }
  
      void insert(std::initializer_list<value_type> ilist) {
          for (auto&& vt : ilist) {
              insert(std::move(vt));
          }
      }
  
      template <typename... Args>
      std::pair<iterator, bool> emplace(Args&&... args) {
          ROBIN_HOOD_TRACE(this)
          Node n{*this, std::forward<Args>(args)...};
          auto idxAndState = insertKeyPrepareEmptySpot(getFirstConst(n));
          switch (idxAndState.second) {
          case InsertionState::key_found:
              n.destroy(*this);
              break;
  
          case InsertionState::new_node:
              ::new (static_cast<void*>(&mKeyVals[idxAndState.first])) Node(*this, std::move(n));
              break;
  
          case InsertionState::overwrite_node:
              mKeyVals[idxAndState.first] = std::move(n);
              break;
  
          case InsertionState::overflow_error:
              n.destroy(*this);
              throwOverflowError();
              break;
          }
  
          return std::make_pair(iterator(mKeyVals + idxAndState.first, mInfo + idxAndState.first),
                                InsertionState::key_found != idxAndState.second);
      }
  
      template <typename... Args>
      std::pair<iterator, bool> try_emplace(const key_type& key, Args&&... args) {
          return try_emplace_impl(key, std::forward<Args>(args)...);
      }
  
      template <typename... Args>
      std::pair<iterator, bool> try_emplace(key_type&& key, Args&&... args) {
          return try_emplace_impl(std::move(key), std::forward<Args>(args)...);
      }
  
      template <typename... Args>
      std::pair<iterator, bool> try_emplace(const_iterator hint, const key_type& key,
                                            Args&&... args) {
          (void)hint;
          return try_emplace_impl(key, std::forward<Args>(args)...);
      }
  
      template <typename... Args>
      std::pair<iterator, bool> try_emplace(const_iterator hint, key_type&& key, Args&&... args) {
          (void)hint;
          return try_emplace_impl(std::move(key), std::forward<Args>(args)...);
      }
  
      template <typename Mapped>
      std::pair<iterator, bool> insert_or_assign(const key_type& key, Mapped&& obj) {
          return insertOrAssignImpl(key, std::forward<Mapped>(obj));
      }
  
      template <typename Mapped>
      std::pair<iterator, bool> insert_or_assign(key_type&& key, Mapped&& obj) {
          return insertOrAssignImpl(std::move(key), std::forward<Mapped>(obj));
      }
  
      template <typename Mapped>
      std::pair<iterator, bool> insert_or_assign(const_iterator hint, const key_type& key,
                                                 Mapped&& obj) {
          (void)hint;
          return insertOrAssignImpl(key, std::forward<Mapped>(obj));
      }
  
      template <typename Mapped>
      std::pair<iterator, bool> insert_or_assign(const_iterator hint, key_type&& key, Mapped&& obj) {
          (void)hint;
          return insertOrAssignImpl(std::move(key), std::forward<Mapped>(obj));
      }
  
      std::pair<iterator, bool> insert(const value_type& keyval) {
          ROBIN_HOOD_TRACE(this)
          return emplace(keyval);
      }
  
      std::pair<iterator, bool> insert(value_type&& keyval) {
          return emplace(std::move(keyval));
      }
  
      // Returns 1 if key is found, 0 otherwise.
      size_t count(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          auto kv = mKeyVals + findIdx(key);
          if (kv != reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
              return 1;
          }
          return 0;
      }
  
      template <typename OtherKey, typename Self_ = Self>
      // NOLINTNEXTLINE(modernize-use-nodiscard)
      typename std::enable_if<Self_::is_transparent, size_t>::type count(const OtherKey& key) const {
          ROBIN_HOOD_TRACE(this)
          auto kv = mKeyVals + findIdx(key);
          if (kv != reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
              return 1;
          }
          return 0;
      }
  
      bool contains(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
          return 1U == count(key);
      }
  
      template <typename OtherKey, typename Self_ = Self>
      // NOLINTNEXTLINE(modernize-use-nodiscard)
      typename std::enable_if<Self_::is_transparent, bool>::type contains(const OtherKey& key) const {
          return 1U == count(key);
      }
  
      // Returns a reference to the value found for key.
      // Throws std::out_of_range if element cannot be found
      template <typename Q = mapped_type>
      // NOLINTNEXTLINE(modernize-use-nodiscard)
      typename std::enable_if<!std::is_void<Q>::value, Q&>::type at(key_type const& key) {
          ROBIN_HOOD_TRACE(this)
          auto kv = mKeyVals + findIdx(key);
          if (kv == reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
              doThrow<std::out_of_range>("key not found");
          }
          return kv->getSecond();
      }
  
      // Returns a reference to the value found for key.
      // Throws std::out_of_range if element cannot be found
      template <typename Q = mapped_type>
      // NOLINTNEXTLINE(modernize-use-nodiscard)
      typename std::enable_if<!std::is_void<Q>::value, Q const&>::type at(key_type const& key) const {
          ROBIN_HOOD_TRACE(this)
          auto kv = mKeyVals + findIdx(key);
          if (kv == reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
              doThrow<std::out_of_range>("key not found");
          }
          return kv->getSecond();
      }
  
      const_iterator find(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return const_iterator{mKeyVals + idx, mInfo + idx};
      }
  
      template <typename OtherKey>
      const_iterator find(const OtherKey& key, is_transparent_tag /*unused*/) const {
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return const_iterator{mKeyVals + idx, mInfo + idx};
      }
  
      template <typename OtherKey, typename Self_ = Self>
      typename std::enable_if<Self_::is_transparent, // NOLINT(modernize-use-nodiscard)
                              const_iterator>::type  // NOLINT(modernize-use-nodiscard)
      find(const OtherKey& key) const {              // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return const_iterator{mKeyVals + idx, mInfo + idx};
      }
  
      iterator find(const key_type& key) {
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return iterator{mKeyVals + idx, mInfo + idx};
      }
  
      template <typename OtherKey>
      iterator find(const OtherKey& key, is_transparent_tag /*unused*/) {
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return iterator{mKeyVals + idx, mInfo + idx};
      }
  
      template <typename OtherKey, typename Self_ = Self>
      typename std::enable_if<Self_::is_transparent, iterator>::type find(const OtherKey& key) {
          ROBIN_HOOD_TRACE(this)
          const size_t idx = findIdx(key);
          return iterator{mKeyVals + idx, mInfo + idx};
      }
  
      iterator begin() {
          ROBIN_HOOD_TRACE(this)
          if (empty()) {
              return end();
          }
          return iterator(mKeyVals, mInfo, fast_forward_tag{});
      }
      const_iterator begin() const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return cbegin();
      }
      const_iterator cbegin() const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          if (empty()) {
              return cend();
          }
          return const_iterator(mKeyVals, mInfo, fast_forward_tag{});
      }
  
      iterator end() {
          ROBIN_HOOD_TRACE(this)
          // no need to supply valid info pointer: end() must not be dereferenced, and only node
          // pointer is compared.
          return iterator{reinterpret_cast_no_cast_align_warning<Node*>(mInfo), nullptr};
      }
      const_iterator end() const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return cend();
      }
      const_iterator cend() const { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return const_iterator{reinterpret_cast_no_cast_align_warning<Node*>(mInfo), nullptr};
      }
  
      iterator erase(const_iterator pos) {
          ROBIN_HOOD_TRACE(this)
          // its safe to perform const cast here
          // NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
          return erase(iterator{const_cast<Node*>(pos.mKeyVals), const_cast<uint8_t*>(pos.mInfo)});
      }
  
      // Erases element at pos, returns iterator to the next element.
      iterator erase(iterator pos) {
          ROBIN_HOOD_TRACE(this)
          // we assume that pos always points to a valid entry, and not end().
          auto const idx = static_cast<size_t>(pos.mKeyVals - mKeyVals);
  
          shiftDown(idx);
          --mNumElements;
  
          if (*pos.mInfo) {
              // we've backward shifted, return this again
              return pos;
          }
  
          // no backward shift, return next element
          return ++pos;
      }
  
      size_t erase(const key_type& key) {
          ROBIN_HOOD_TRACE(this)
          size_t idx{};
          InfoType info{};
          keyToIdx(key, &idx, &info);
  
          // check while info matches with the source idx
          do {
              if (info == mInfo[idx] && WKeyEqual::operator()(key, mKeyVals[idx].getFirst())) {
                  shiftDown(idx);
                  --mNumElements;
                  return 1;
              }
              next(&info, &idx);
          } while (info <= mInfo[idx]);
  
          // nothing found to delete
          return 0;
      }
  
      // reserves space for the specified number of elements. Makes sure the old data fits.
      // exactly the same as reserve(c).
      void rehash(size_t c) {
          // forces a reserve
          reserve(c, true);
      }
  
      // reserves space for the specified number of elements. Makes sure the old data fits.
      // Exactly the same as rehash(c). Use rehash(0) to shrink to fit.
      void reserve(size_t c) {
          // reserve, but don't force rehash
          reserve(c, false);
      }
  
      // If possible reallocates the map to a smaller one. This frees the underlying table.
      // Does not do anything if load_factor is too large for decreasing the table's size.
      void compact() {
          ROBIN_HOOD_TRACE(this)
          auto newSize = InitialNumElements;
          while (calcMaxNumElementsAllowed(newSize) < mNumElements && newSize != 0) {
              newSize *= 2;
          }
          if (ROBIN_HOOD_UNLIKELY(newSize == 0)) {
              throwOverflowError();
          }
  
          ROBIN_HOOD_LOG("newSize > mMask + 1: " << newSize << " > " << mMask << " + 1")
  
          // only actually do anything when the new size is bigger than the old one. This prevents to
          // continuously allocate for each reserve() call.
          if (newSize < mMask + 1) {
              rehashPowerOfTwo(newSize, true);
          }
      }
  
      size_type size() const noexcept { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return mNumElements;
      }
  
      size_type max_size() const noexcept { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return static_cast<size_type>(-1);
      }
  
      ROBIN_HOOD(NODISCARD) bool empty() const noexcept {
          ROBIN_HOOD_TRACE(this)
          return 0 == mNumElements;
      }
  
      float max_load_factor() const noexcept { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return MaxLoadFactor100 / 100.0F;
      }
  
      // Average number of elements per bucket. Since we allow only 1 per bucket
      float load_factor() const noexcept { // NOLINT(modernize-use-nodiscard)
          ROBIN_HOOD_TRACE(this)
          return static_cast<float>(size()) / static_cast<float>(mMask + 1);
      }
  
      ROBIN_HOOD(NODISCARD) size_t mask() const noexcept {
          ROBIN_HOOD_TRACE(this)
          return mMask;
      }
  
      ROBIN_HOOD(NODISCARD) size_t calcMaxNumElementsAllowed(size_t maxElements) const noexcept {
          if (ROBIN_HOOD_LIKELY(maxElements <= (std::numeric_limits<size_t>::max)() / 100)) {
              return maxElements * MaxLoadFactor100 / 100;
          }
  
          // we might be a bit inprecise, but since maxElements is quite large that doesn't matter
          return (maxElements / 100) * MaxLoadFactor100;
      }
  
      ROBIN_HOOD(NODISCARD) size_t calcNumBytesInfo(size_t numElements) const noexcept {
          // we add a uint64_t, which houses the sentinel (first byte) and padding so we can load
          // 64bit types.
          return numElements + sizeof(uint64_t);
      }
  
      ROBIN_HOOD(NODISCARD)
      size_t calcNumElementsWithBuffer(size_t numElements) const noexcept {
          auto maxNumElementsAllowed = calcMaxNumElementsAllowed(numElements);
          return numElements + (std::min)(maxNumElementsAllowed, (static_cast<size_t>(0xFF)));
      }
  
      // calculation only allowed for 2^n values
      ROBIN_HOOD(NODISCARD) size_t calcNumBytesTotal(size_t numElements) const {
  #if ROBIN_HOOD(BITNESS) == 64
          return numElements * sizeof(Node) + calcNumBytesInfo(numElements);
  #else
          // make sure we're doing 64bit operations, so we are at least safe against 32bit overflows.
          auto const ne = static_cast<uint64_t>(numElements);
          auto const s = static_cast<uint64_t>(sizeof(Node));
          auto const infos = static_cast<uint64_t>(calcNumBytesInfo(numElements));
  
          auto const total64 = ne * s + infos;
          auto const total = static_cast<size_t>(total64);
  
          if (ROBIN_HOOD_UNLIKELY(static_cast<uint64_t>(total) != total64)) {
              throwOverflowError();
          }
          return total;
  #endif
      }
  
  private:
      template <typename Q = mapped_type>
      ROBIN_HOOD(NODISCARD)
      typename std::enable_if<!std::is_void<Q>::value, bool>::type has(const value_type& e) const {
          ROBIN_HOOD_TRACE(this)
          auto it = find(e.first);
          return it != end() && it->second == e.second;
      }
  
      template <typename Q = mapped_type>
      ROBIN_HOOD(NODISCARD)
      typename std::enable_if<std::is_void<Q>::value, bool>::type has(const value_type& e) const {
          ROBIN_HOOD_TRACE(this)
          return find(e) != end();
      }
  
      void reserve(size_t c, bool forceRehash) {
          ROBIN_HOOD_TRACE(this)
          auto const minElementsAllowed = (std::max)(c, mNumElements);
          auto newSize = InitialNumElements;
          while (calcMaxNumElementsAllowed(newSize) < minElementsAllowed && newSize != 0) {
              newSize *= 2;
          }
          if (ROBIN_HOOD_UNLIKELY(newSize == 0)) {
              throwOverflowError();
          }
  
          ROBIN_HOOD_LOG("newSize > mMask + 1: " << newSize << " > " << mMask << " + 1")
  
          // only actually do anything when the new size is bigger than the old one. This prevents to
          // continuously allocate for each reserve() call.
          if (forceRehash || newSize > mMask + 1) {
              rehashPowerOfTwo(newSize, false);
          }
      }
  
      // reserves space for at least the specified number of elements.
      // only works if numBuckets if power of two
      // True on success, false otherwise
      void rehashPowerOfTwo(size_t numBuckets, bool forceFree) {
          ROBIN_HOOD_TRACE(this)
  
          Node* const oldKeyVals = mKeyVals;
          uint8_t const* const oldInfo = mInfo;
  
          const size_t oldMaxElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);
  
          // resize operation: move stuff
          initData(numBuckets);
          if (oldMaxElementsWithBuffer > 1) {
              for (size_t i = 0; i < oldMaxElementsWithBuffer; ++i) {
                  if (oldInfo[i] != 0) {
                      // might throw an exception, which is really bad since we are in the middle of
                      // moving stuff.
                      insert_move(std::move(oldKeyVals[i]));
                      // destroy the node but DON'T destroy the data.
                      oldKeyVals[i].~Node();
                  }
              }
  
              // this check is not necessary as it's guarded by the previous if, but it helps
              // silence g++'s overeager "attempt to free a non-heap object 'map'
              // [-Werror=free-nonheap-object]" warning.
              if (oldKeyVals != reinterpret_cast_no_cast_align_warning<Node*>(&mMask)) {
                  // don't destroy old data: put it into the pool instead
                  if (forceFree) {
                      std::free(oldKeyVals);
                  } else {
                      DataPool::addOrFree(oldKeyVals, calcNumBytesTotal(oldMaxElementsWithBuffer));
                  }
              }
          }
      }
  
      ROBIN_HOOD(NOINLINE) void throwOverflowError() const {
  #if ROBIN_HOOD(HAS_EXCEPTIONS)
          throw std::overflow_error("robin_hood::map overflow");
  #else
          abort();
  #endif
      }
  
      template <typename OtherKey, typename... Args>
      std::pair<iterator, bool> try_emplace_impl(OtherKey&& key, Args&&... args) {
          ROBIN_HOOD_TRACE(this)
          auto idxAndState = insertKeyPrepareEmptySpot(key);
          switch (idxAndState.second) {
          case InsertionState::key_found:
              break;
  
          case InsertionState::new_node:
              ::new (static_cast<void*>(&mKeyVals[idxAndState.first])) Node(
                  *this, std::piecewise_construct, std::forward_as_tuple(std::forward<OtherKey>(key)),
                  std::forward_as_tuple(std::forward<Args>(args)...));
              break;
  
          case InsertionState::overwrite_node:
              mKeyVals[idxAndState.first] = Node(*this, std::piecewise_construct,
                                                 std::forward_as_tuple(std::forward<OtherKey>(key)),
                                                 std::forward_as_tuple(std::forward<Args>(args)...));
              break;
  
          case InsertionState::overflow_error:
              throwOverflowError();
              break;
          }
  
          return std::make_pair(iterator(mKeyVals + idxAndState.first, mInfo + idxAndState.first),
                                InsertionState::key_found != idxAndState.second);
      }
  
      template <typename OtherKey, typename Mapped>
      std::pair<iterator, bool> insertOrAssignImpl(OtherKey&& key, Mapped&& obj) {
          ROBIN_HOOD_TRACE(this)
          auto idxAndState = insertKeyPrepareEmptySpot(key);
          switch (idxAndState.second) {
          case InsertionState::key_found:
              mKeyVals[idxAndState.first].getSecond() = std::forward<Mapped>(obj);
              break;
  
          case InsertionState::new_node:
              ::new (static_cast<void*>(&mKeyVals[idxAndState.first])) Node(
                  *this, std::piecewise_construct, std::forward_as_tuple(std::forward<OtherKey>(key)),
                  std::forward_as_tuple(std::forward<Mapped>(obj)));
              break;
  
          case InsertionState::overwrite_node:
              mKeyVals[idxAndState.first] = Node(*this, std::piecewise_construct,
                                                 std::forward_as_tuple(std::forward<OtherKey>(key)),
                                                 std::forward_as_tuple(std::forward<Mapped>(obj)));
              break;
  
          case InsertionState::overflow_error:
              throwOverflowError();
              break;
          }
  
          return std::make_pair(iterator(mKeyVals + idxAndState.first, mInfo + idxAndState.first),
                                InsertionState::key_found != idxAndState.second);
      }
  
      void initData(size_t max_elements) {
          mNumElements = 0;
          mMask = max_elements - 1;
          mMaxNumElementsAllowed = calcMaxNumElementsAllowed(max_elements);
  
          auto const numElementsWithBuffer = calcNumElementsWithBuffer(max_elements);
  
          // calloc also zeroes everything
          auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);
          ROBIN_HOOD_LOG("std::calloc " << numBytesTotal << " = calcNumBytesTotal("
                                        << numElementsWithBuffer << ")")
          mKeyVals = reinterpret_cast<Node*>(
              detail::assertNotNull<std::bad_alloc>(std::calloc(1, numBytesTotal)));
          mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);
  
          // set sentinel
          mInfo[numElementsWithBuffer] = 1;
  
          mInfoInc = InitialInfoInc;
          mInfoHashShift = InitialInfoHashShift;
      }
  
      enum class InsertionState { overflow_error, key_found, new_node, overwrite_node };
  
      // Finds key, and if not already present prepares a spot where to pot the key & value.
      // This potentially shifts nodes out of the way, updates mInfo and number of inserted
      // elements, so the only operation left to do is create/assign a new node at that spot.
      template <typename OtherKey>
      std::pair<size_t, InsertionState> insertKeyPrepareEmptySpot(OtherKey&& key) {
          for (int i = 0; i < 256; ++i) {
              size_t idx{};
              InfoType info{};
              keyToIdx(key, &idx, &info);
              nextWhileLess(&info, &idx);
  
              // while we potentially have a match
              while (info == mInfo[idx]) {
                  if (WKeyEqual::operator()(key, mKeyVals[idx].getFirst())) {
                      // key already exists, do NOT insert.
                      // see http://en.cppreference.com/w/cpp/container/unordered_map/insert
                      return std::make_pair(idx, InsertionState::key_found);
                  }
                  next(&info, &idx);
              }
  
              // unlikely that this evaluates to true
              if (ROBIN_HOOD_UNLIKELY(mNumElements >= mMaxNumElementsAllowed)) {
                  if (!increase_size()) {
                      return std::make_pair(size_t(0), InsertionState::overflow_error);
                  }
                  continue;
              }
  
              // key not found, so we are now exactly where we want to insert it.
              auto const insertion_idx = idx;
              auto const insertion_info = info;
              if (ROBIN_HOOD_UNLIKELY(insertion_info + mInfoInc > 0xFF)) {
                  mMaxNumElementsAllowed = 0;
              }
  
              // find an empty spot
              while (0 != mInfo[idx]) {
                  next(&info, &idx);
              }
  
              if (idx != insertion_idx) {
                  shiftUp(idx, insertion_idx);
              }
              // put at empty spot
              mInfo[insertion_idx] = static_cast<uint8_t>(insertion_info);
              ++mNumElements;
              return std::make_pair(insertion_idx, idx == insertion_idx
                                                       ? InsertionState::new_node
                                                       : InsertionState::overwrite_node);
          }
  
          // enough attempts failed, so finally give up.
          return std::make_pair(size_t(0), InsertionState::overflow_error);
      }
  
      bool try_increase_info() {
          ROBIN_HOOD_LOG("mInfoInc=" << mInfoInc << ", numElements=" << mNumElements
                                     << ", maxNumElementsAllowed="
                                     << calcMaxNumElementsAllowed(mMask + 1))
          if (mInfoInc <= 2) {
              // need to be > 2 so that shift works (otherwise undefined behavior!)
              return false;
          }
          // we got space left, try to make info smaller
          mInfoInc = static_cast<uint8_t>(mInfoInc >> 1U);
  
          // remove one bit of the hash, leaving more space for the distance info.
          // This is extremely fast because we can operate on 8 bytes at once.
          ++mInfoHashShift;
          auto const numElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);
  
          for (size_t i = 0; i < numElementsWithBuffer; i += 8) {
              auto val = unaligned_load<uint64_t>(mInfo + i);
              val = (val >> 1U) & UINT64_C(0x7f7f7f7f7f7f7f7f);
              std::memcpy(mInfo + i, &val, sizeof(val));
          }
          // update sentinel, which might have been cleared out!
          mInfo[numElementsWithBuffer] = 1;
  
          mMaxNumElementsAllowed = calcMaxNumElementsAllowed(mMask + 1);
          return true;
      }
  
      // True if resize was possible, false otherwise
      bool increase_size() {
          // nothing allocated yet? just allocate InitialNumElements
          if (0 == mMask) {
              initData(InitialNumElements);
              return true;
          }
  
          auto const maxNumElementsAllowed = calcMaxNumElementsAllowed(mMask + 1);
          if (mNumElements < maxNumElementsAllowed && try_increase_info()) {
              return true;
          }
  
          ROBIN_HOOD_LOG("mNumElements=" << mNumElements << ", maxNumElementsAllowed="
                                         << maxNumElementsAllowed << ", load="
                                         << (static_cast<double>(mNumElements) * 100.0 /
                                             (static_cast<double>(mMask) + 1)))
  
          if (mNumElements * 2 < calcMaxNumElementsAllowed(mMask + 1)) {
              // we have to resize, even though there would still be plenty of space left!
              // Try to rehash instead. Delete freed memory so we don't steadyily increase mem in case
              // we have to rehash a few times
              nextHashMultiplier();
              rehashPowerOfTwo(mMask + 1, true);
          } else {
              // we've reached the capacity of the map, so the hash seems to work nice. Keep using it.
              rehashPowerOfTwo((mMask + 1) * 2, false);
          }
          return true;
      }
  
      void nextHashMultiplier() {
          // adding an *even* number, so that the multiplier will always stay odd. This is necessary
          // so that the hash stays a mixing function (and thus doesn't have any information loss).
          mHashMultiplier += UINT64_C(0xc4ceb9fe1a85ec54);
      }
  
      void destroy() {
          if (0 == mMask) {
              // don't deallocate!
              return;
          }
  
          Destroyer<Self, IsFlat && std::is_trivially_destructible<Node>::value>{}
              .nodesDoNotDeallocate(*this);
  
          // This protection against not deleting mMask shouldn't be needed as it's sufficiently
          // protected with the 0==mMask check, but I have this anyways because g++ 7 otherwise
          // reports a compile error: attempt to free a non-heap object 'fm'
          // [-Werror=free-nonheap-object]
          if (mKeyVals != reinterpret_cast_no_cast_align_warning<Node*>(&mMask)) {
              ROBIN_HOOD_LOG("std::free")
              std::free(mKeyVals);
          }
      }
  
      void init() noexcept {
          mKeyVals = reinterpret_cast_no_cast_align_warning<Node*>(&mMask);
          mInfo = reinterpret_cast<uint8_t*>(&mMask);
          mNumElements = 0;
          mMask = 0;
          mMaxNumElementsAllowed = 0;
          mInfoInc = InitialInfoInc;
          mInfoHashShift = InitialInfoHashShift;
      }
  
      // members are sorted so no padding occurs
      uint64_t mHashMultiplier = UINT64_C(0xc4ceb9fe1a85ec53);                // 8 byte  8
      Node* mKeyVals = reinterpret_cast_no_cast_align_warning<Node*>(&mMask); // 8 byte 16
      uint8_t* mInfo = reinterpret_cast<uint8_t*>(&mMask);                    // 8 byte 24
      size_t mNumElements = 0;                                                // 8 byte 32
      size_t mMask = 0;                                                       // 8 byte 40
      size_t mMaxNumElementsAllowed = 0;                                      // 8 byte 48
      InfoType mInfoInc = InitialInfoInc;                                     // 4 byte 52
      InfoType mInfoHashShift = InitialInfoHashShift;                         // 4 byte 56
                                                      // 16 byte 56 if NodeAllocator
  };
  
  } // namespace detail
  
  // map
  
  template <typename Key, typename T, typename Hash = hash<Key>,
            typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
  using unordered_flat_map = detail::Table<true, MaxLoadFactor100, Key, T, Hash, KeyEqual>;
  
  template <typename Key, typename T, typename Hash = hash<Key>,
            typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
  using unordered_node_map = detail::Table<false, MaxLoadFactor100, Key, T, Hash, KeyEqual>;
  
  template <typename Key, typename T, typename Hash = hash<Key>,
            typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
  using unordered_map =
      detail::Table<sizeof(robin_hood::pair<Key, T>) <= sizeof(size_t) * 6 &&
                        std::is_nothrow_move_constructible<robin_hood::pair<Key, T>>::value &&
                        std::is_nothrow_move_assignable<robin_hood::pair<Key, T>>::value,
                    MaxLoadFactor100, Key, T, Hash, KeyEqual>;
  
  // set
  
  template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
            size_t MaxLoadFactor100 = 80>
  using unordered_flat_set = detail::Table<true, MaxLoadFactor100, Key, void, Hash, KeyEqual>;
  
  template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
            size_t MaxLoadFactor100 = 80>
  using unordered_node_set = detail::Table<false, MaxLoadFactor100, Key, void, Hash, KeyEqual>;
  
  template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
            size_t MaxLoadFactor100 = 80>
  using unordered_set = detail::Table<sizeof(Key) <= sizeof(size_t) * 6 &&
                                          std::is_nothrow_move_constructible<Key>::value &&
                                          std::is_nothrow_move_assignable<Key>::value,
                                      MaxLoadFactor100, Key, void, Hash, KeyEqual>;
  
  } // namespace robin_hood
  
  #endif