text: //===--- ArrayRef.h - Array Reference Wrapper -------------------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ADT_ARRAYREF_H
  #define LLVM_ADT_ARRAYREF_H
  
  #include "llvm/ADT/Hashing.h"
  #include "llvm/ADT/None.h"
  #include "llvm/ADT/SmallVector.h"
  #include <vector>
  
  namespace llvm {
    /// ArrayRef - Represent a constant reference to an array (0 or more elements
    /// consecutively in memory), i.e. a start pointer and a length.  It allows
    /// various APIs to take consecutive elements easily and conveniently.
    ///
    /// This class does not own the underlying data, it is expected to be used in
    /// situations where the data resides in some other buffer, whose lifetime
    /// extends past that of the ArrayRef. For this reason, it is not in general
    /// safe to store an ArrayRef.
    ///
    /// This is intended to be trivially copyable, so it should be passed by
    /// value.
    template<typename T>
    class ArrayRef {
    public:
      typedef const T *iterator;
      typedef const T *const_iterator;
      typedef size_t size_type;
  
      typedef std::reverse_iterator<iterator> reverse_iterator;
  
    private:
      /// The start of the array, in an external buffer.
      const T *Data;
  
      /// The number of elements.
      size_type Length;
  
    public:
      /// @name Constructors
      /// @{
  
      /// Construct an empty ArrayRef.
      /*implicit*/ ArrayRef() : Data(nullptr), Length(0) {}
  
      /// Construct an empty ArrayRef from None.
      /*implicit*/ ArrayRef(NoneType) : Data(nullptr), Length(0) {}
  
      /// Construct an ArrayRef from a single element.
      /*implicit*/ ArrayRef(const T &OneElt)
        : Data(&OneElt), Length(1) {}
  
      /// Construct an ArrayRef from a pointer and length.
      /*implicit*/ ArrayRef(const T *data, size_t length)
        : Data(data), Length(length) {}
  
      /// Construct an ArrayRef from a range.
      ArrayRef(const T *begin, const T *end)
        : Data(begin), Length(end - begin) {}
  
      /// Construct an ArrayRef from a SmallVector. This is templated in order to
      /// avoid instantiating SmallVectorTemplateCommon<T> whenever we
      /// copy-construct an ArrayRef.
      template<typename U>
      /*implicit*/ ArrayRef(const SmallVectorTemplateCommon<T, U> &Vec)
        : Data(Vec.data()), Length(Vec.size()) {
      }
  
      /// Construct an ArrayRef from a std::vector.
      template<typename A>
      /*implicit*/ ArrayRef(const std::vector<T, A> &Vec)
        : Data(Vec.data()), Length(Vec.size()) {}
  
      /// Construct an ArrayRef from a C array.
      template <size_t N>
      /*implicit*/ LLVM_CONSTEXPR ArrayRef(const T (&Arr)[N])
        : Data(Arr), Length(N) {}
  
      /// Construct an ArrayRef from a std::initializer_list.
      /*implicit*/ ArrayRef(const std::initializer_list<T> &Vec)
      : Data(Vec.begin() == Vec.end() ? (T*)nullptr : Vec.begin()),
        Length(Vec.size()) {}
  
      /// Construct an ArrayRef<const T*> from ArrayRef<T*>. This uses SFINAE to
      /// ensure that only ArrayRefs of pointers can be converted.
      template <typename U>
      ArrayRef(
          const ArrayRef<U *> &A,
          typename std::enable_if<
             std::is_convertible<U *const *, T const *>::value>::type * = nullptr)
        : Data(A.data()), Length(A.size()) {}
  
      /// Construct an ArrayRef<const T*> from a SmallVector<T*>. This is
      /// templated in order to avoid instantiating SmallVectorTemplateCommon<T>
      /// whenever we copy-construct an ArrayRef.
      template<typename U, typename DummyT>
      /*implicit*/ ArrayRef(
        const SmallVectorTemplateCommon<U *, DummyT> &Vec,
        typename std::enable_if<
            std::is_convertible<U *const *, T const *>::value>::type * = nullptr)
        : Data(Vec.data()), Length(Vec.size()) {
      }
  
      /// Construct an ArrayRef<const T*> from std::vector<T*>. This uses SFINAE
      /// to ensure that only vectors of pointers can be converted.
      template<typename U, typename A>
      ArrayRef(const std::vector<U *, A> &Vec,
               typename std::enable_if<
                   std::is_convertible<U *const *, T const *>::value>::type* = 0)
        : Data(Vec.data()), Length(Vec.size()) {}
  
      /// @}
      /// @name Simple Operations
      /// @{
  
      iterator begin() const { return Data; }
      iterator end() const { return Data + Length; }
  
      reverse_iterator rbegin() const { return reverse_iterator(end()); }
      reverse_iterator rend() const { return reverse_iterator(begin()); }
  
      /// empty - Check if the array is empty.
      bool empty() const { return Length == 0; }
  
      const T *data() const { return Data; }
  
      /// size - Get the array size.
      size_t size() const { return Length; }
  
      /// front - Get the first element.
      const T &front() const {
        assert(!empty());
        return Data[0];
      }
  
      /// back - Get the last element.
      const T &back() const {
        assert(!empty());
        return Data[Length-1];
      }
  
      // copy - Allocate copy in Allocator and return ArrayRef<T> to it.
      template <typename Allocator> ArrayRef<T> copy(Allocator &A) {
        T *Buff = A.template Allocate<T>(Length);
        std::uninitialized_copy(begin(), end(), Buff);
        return ArrayRef<T>(Buff, Length);
      }
  
      /// equals - Check for element-wise equality.
      bool equals(ArrayRef RHS) const {
        if (Length != RHS.Length)
          return false;
        return std::equal(begin(), end(), RHS.begin());
      }
  
      /// slice(n) - Chop off the first N elements of the array.
      ArrayRef<T> slice(unsigned N) const {
        assert(N <= size() && "Invalid specifier");
        return ArrayRef<T>(data()+N, size()-N);
      }
  
      /// slice(n, m) - Chop off the first N elements of the array, and keep M
      /// elements in the array.
      ArrayRef<T> slice(unsigned N, unsigned M) const {
        assert(N+M <= size() && "Invalid specifier");
        return ArrayRef<T>(data()+N, M);
      }
  
      // \brief Drop the last \p N elements of the array.
      ArrayRef<T> drop_back(unsigned N = 1) const {
        assert(size() >= N && "Dropping more elements than exist");
        return slice(0, size() - N);
      }
  
      /// @}
      /// @name Operator Overloads
      /// @{
      const T &operator[](size_t Index) const {
        assert(Index < Length && "Invalid index!");
        return Data[Index];
      }
  
      /// @}
      /// @name Expensive Operations
      /// @{
      std::vector<T> vec() const {
        return std::vector<T>(Data, Data+Length);
      }
  
      /// @}
      /// @name Conversion operators
      /// @{
      operator std::vector<T>() const {
        return std::vector<T>(Data, Data+Length);
      }
  
      /// @}
    };
  
    /// MutableArrayRef - Represent a mutable reference to an array (0 or more
    /// elements consecutively in memory), i.e. a start pointer and a length.  It
    /// allows various APIs to take and modify consecutive elements easily and
    /// conveniently.
    ///
    /// This class does not own the underlying data, it is expected to be used in
    /// situations where the data resides in some other buffer, whose lifetime
    /// extends past that of the MutableArrayRef. For this reason, it is not in
    /// general safe to store a MutableArrayRef.
    ///
    /// This is intended to be trivially copyable, so it should be passed by
    /// value.
    template<typename T>
    class MutableArrayRef : public ArrayRef<T> {
    public:
      typedef T *iterator;
  
      typedef std::reverse_iterator<iterator> reverse_iterator;
  
      /// Construct an empty MutableArrayRef.
      /*implicit*/ MutableArrayRef() : ArrayRef<T>() {}
  
      /// Construct an empty MutableArrayRef from None.
      /*implicit*/ MutableArrayRef(NoneType) : ArrayRef<T>() {}
  
      /// Construct an MutableArrayRef from a single element.
      /*implicit*/ MutableArrayRef(T &OneElt) : ArrayRef<T>(OneElt) {}
  
      /// Construct an MutableArrayRef from a pointer and length.
      /*implicit*/ MutableArrayRef(T *data, size_t length)
        : ArrayRef<T>(data, length) {}
  
      /// Construct an MutableArrayRef from a range.
      MutableArrayRef(T *begin, T *end) : ArrayRef<T>(begin, end) {}
  
      /// Construct an MutableArrayRef from a SmallVector.
      /*implicit*/ MutableArrayRef(SmallVectorImpl<T> &Vec)
      : ArrayRef<T>(Vec) {}
  
      /// Construct a MutableArrayRef from a std::vector.
      /*implicit*/ MutableArrayRef(std::vector<T> &Vec)
      : ArrayRef<T>(Vec) {}
  
      /// Construct an MutableArrayRef from a C array.
      template <size_t N>
      /*implicit*/ LLVM_CONSTEXPR MutableArrayRef(T (&Arr)[N])
        : ArrayRef<T>(Arr) {}
  
      T *data() const { return const_cast<T*>(ArrayRef<T>::data()); }
  
      iterator begin() const { return data(); }
      iterator end() const { return data() + this->size(); }
  
      reverse_iterator rbegin() const { return reverse_iterator(end()); }
      reverse_iterator rend() const { return reverse_iterator(begin()); }
  
      /// front - Get the first element.
      T &front() const {
        assert(!this->empty());
        return data()[0];
      }
  
      /// back - Get the last element.
      T &back() const {
        assert(!this->empty());
        return data()[this->size()-1];
      }
  
      /// slice(n) - Chop off the first N elements of the array.
      MutableArrayRef<T> slice(unsigned N) const {
        assert(N <= this->size() && "Invalid specifier");
        return MutableArrayRef<T>(data()+N, this->size()-N);
      }
  
      /// slice(n, m) - Chop off the first N elements of the array, and keep M
      /// elements in the array.
      MutableArrayRef<T> slice(unsigned N, unsigned M) const {
        assert(N+M <= this->size() && "Invalid specifier");
        return MutableArrayRef<T>(data()+N, M);
      }
  
      MutableArrayRef<T> drop_back(unsigned N) const {
        assert(this->size() >= N && "Dropping more elements than exist");
        return slice(0, this->size() - N);
      }
  
      /// @}
      /// @name Operator Overloads
      /// @{
      T &operator[](size_t Index) const {
        assert(Index < this->size() && "Invalid index!");
        return data()[Index];
      }
    };
  
    /// @name ArrayRef Convenience constructors
    /// @{
  
    /// Construct an ArrayRef from a single element.
    template<typename T>
    ArrayRef<T> makeArrayRef(const T &OneElt) {
      return OneElt;
    }
  
    /// Construct an ArrayRef from a pointer and length.
    template<typename T>
    ArrayRef<T> makeArrayRef(const T *data, size_t length) {
      return ArrayRef<T>(data, length);
    }
  
    /// Construct an ArrayRef from a range.
    template<typename T>
    ArrayRef<T> makeArrayRef(const T *begin, const T *end) {
      return ArrayRef<T>(begin, end);
    }
  
    /// Construct an ArrayRef from a SmallVector.
    template <typename T>
    ArrayRef<T> makeArrayRef(const SmallVectorImpl<T> &Vec) {
      return Vec;
    }
  
    /// Construct an ArrayRef from a SmallVector.
    template <typename T, unsigned N>
    ArrayRef<T> makeArrayRef(const SmallVector<T, N> &Vec) {
      return Vec;
    }
  
    /// Construct an ArrayRef from a std::vector.
    template<typename T>
    ArrayRef<T> makeArrayRef(const std::vector<T> &Vec) {
      return Vec;
    }
  
    /// Construct an ArrayRef from an ArrayRef (no-op) (const)
    template <typename T> ArrayRef<T> makeArrayRef(const ArrayRef<T> &Vec) {
      return Vec;
    }
  
    /// Construct an ArrayRef from an ArrayRef (no-op)
    template <typename T> ArrayRef<T> &makeArrayRef(ArrayRef<T> &Vec) {
      return Vec;
    }
  
    /// Construct an ArrayRef from a C array.
    template<typename T, size_t N>
    ArrayRef<T> makeArrayRef(const T (&Arr)[N]) {
      return ArrayRef<T>(Arr);
    }
  
    /// @}
    /// @name ArrayRef Comparison Operators
    /// @{
  
    template<typename T>
    inline bool operator==(ArrayRef<T> LHS, ArrayRef<T> RHS) {
      return LHS.equals(RHS);
    }
  
    template<typename T>
    inline bool operator!=(ArrayRef<T> LHS, ArrayRef<T> RHS) {
      return !(LHS == RHS);
    }
  
    /// @}
  
    // ArrayRefs can be treated like a POD type.
    template <typename T> struct isPodLike;
    template <typename T> struct isPodLike<ArrayRef<T> > {
      static const bool value = true;
    };
  
    template <typename T> hash_code hash_value(ArrayRef<T> S) {
      return hash_combine_range(S.begin(), S.end());
    }
  } // end namespace llvm
  
  #endif // LLVM_ADT_ARRAYREF_H
  