23 Algorithms library [algorithms]

23.9 Generalized numeric operations [numeric.ops]

23.9.3 Inner product [inner.product]

template<class InputIterator1, class InputIterator2, class T>
  T inner_product(InputIterator1 first1, InputIterator1 last1,
                  InputIterator2 first2, T init);
template<class InputIterator1, class InputIterator2, class T,
         class BinaryOperation1, class BinaryOperation2>
  T inner_product(InputIterator1 first1, InputIterator1 last1,
                  InputIterator2 first2, T init,
                  BinaryOperation1 binary_op1,
                  BinaryOperation2 binary_op2);

Requires: T shall satisfy the Cpp17CopyConstructible (Table 26) and Cpp17CopyAssignable (Table 28) requirements.

In the ranges [first1, last1] and [first2, first2 + (last1 - first1)] binary_op1 and binary_op2 shall neither modify elements nor invalidate iterators or subranges.243

Effects: Computes its result by initializing the accumulator acc with the initial value init and then modifying it with acc = std::move(acc) + (*i1) * (*i2) or acc = binary_op1(std::move(acc), binary_op2(*i1, *i2)) for every iterator i1 in the range [first1, last1) and iterator i2 in the range [first2, first2 + (last1 - first1)) in order.

243)

The use of fully closed ranges is intentional.