text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  // UNSUPPORTED: c++03, c++11, c++14
  
  // <numeric>
  
  // Became constexpr in C++20
  // template<class InputIterator, class OutputIterator, class T,
  //          class BinaryOperation, class UnaryOperation>
  //   OutputIterator transform_inclusive_scan(InputIterator first, InputIterator last,
  //                                           OutputIterator result,
  //                                           BinaryOperation binary_op,
  //                                           UnaryOperation unary_op);
  
  
  #include <numeric>
  #include <algorithm>
  #include <array>
  #include <cassert>
  #include <functional>
  #include <iterator>
  
  #include "test_macros.h"
  #include "test_iterators.h"
  
  struct add_one {
      template <typename T>
      constexpr T operator()(T x) const {
          return x + 1;
      }
  };
  
  template <class Iter1, class BOp, class UOp, class T>
  TEST_CONSTEXPR_CXX20 void
  test(Iter1 first, Iter1 last, BOp bop, UOp uop, const T *rFirst, const T *rLast)
  {
      assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
      T out[5];
  
      // Not in place
      T *end = std::transform_inclusive_scan(first, last, out, bop, uop);
      assert(std::equal(out, end, rFirst, rLast));
  
      // In place
      std::copy(first, last, out);
      end = std::transform_inclusive_scan(out, end, out, bop, uop);
      assert(std::equal(out, end, rFirst, rLast));
  }
  
  
  template <class Iter>
  TEST_CONSTEXPR_CXX20 void
  test()
  {
      int ia[]           = {  1,  3,   5,   7,    9 };
      const int pResI0[] = {  2,  6,  12,  20,   30 };        // with add_one
      const int mResI0[] = {  2,  8, 48,  384, 3840 };
      const int pResN0[] = { -1, -4,  -9, -16,  -25 };        // with negate
      const int mResN0[] = { -1,  3, -15, 105, -945 };
      const unsigned sa = sizeof(ia) / sizeof(ia[0] );
      static_assert(sa == sizeof(pResI0) / sizeof(pResI0[0]));       // just to be sure
      static_assert(sa == sizeof(mResI0) / sizeof(mResI0[0]));       // just to be sure
      static_assert(sa == sizeof(pResN0) / sizeof(pResN0[0]));       // just to be sure
      static_assert(sa == sizeof(mResN0) / sizeof(mResN0[0]));       // just to be sure
  
      for (unsigned int i = 0; i < sa; ++i ) {
          test(Iter(ia), Iter(ia + i), std::plus<>(),       add_one{},       pResI0, pResI0 + i);
          test(Iter(ia), Iter(ia + i), std::multiplies<>(), add_one{},       mResI0, mResI0 + i);
          test(Iter(ia), Iter(ia + i), std::plus<>(),       std::negate<>(), pResN0, pResN0 + i);
          test(Iter(ia), Iter(ia + i), std::multiplies<>(), std::negate<>(), mResN0, mResN0 + i);
      }
  }
  
  constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
  
  //  Basic sanity
  TEST_CONSTEXPR_CXX20 void
  basic_tests()
  {
      {
      std::array<size_t, 10> v;
      std::fill(v.begin(), v.end(), 3);
      std::transform_inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), add_one{});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == (i+1) * 4);
      }
  
      {
      std::array<size_t, 10> v;
      std::iota(v.begin(), v.end(), 0);
      std::transform_inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), add_one{});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == triangle(i) + i + 1);
      }
  
      {
      std::array<size_t, 10> v;
      std::iota(v.begin(), v.end(), 1);
      std::transform_inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), add_one{});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == triangle(i + 1) + i + 1);
      }
  
      {
      std::array<size_t, 0> v, res;
      std::transform_inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>(), add_one{});
      assert(res.empty());
      }
  }
  
  TEST_CONSTEXPR_CXX20 bool
  test()
  {
      basic_tests();
  
  //  All the iterator categories
      test<cpp17_input_iterator        <const int*> >();
      test<forward_iterator      <const int*> >();
      test<bidirectional_iterator<const int*> >();
      test<random_access_iterator<const int*> >();
      test<const int*>();
      test<      int*>();
  
      return true;
  }
  
  int main(int, char**)
  {
      test();
  #if TEST_STD_VER > 17
      static_assert(test());
  #endif
      return 0;
  }
  