Why has std::accumulate not been made constexpr in C++20?

Question

In C++20, many (most?) C++-standard-library algorithms have been made constexpr. Yet - std::accumulate has not.

It seems like it could have been:

template<class InputIt, class T>
constexpr T accumulate(InputIt first, InputIt last, T init)
{
    for (; first != last; ++first) {
        init = std::move(init) + *first;
    }
    return init;
}

So - is there a reason it wasn't constexpr'ed as well?

Note: This question was motivated by my answer to this question on compile-time accumulation.

Answer 1

P1645R1 was actually adopted in the Belfast meeting for inclusion in C++20 in response to NB comment US 320.

As a result, all of the following algorithms will be constexpr in C++20 (except for the overloads of them that take an ExecutionPolicy):

• accumulate
• reduce
• inner_product
• transform_reduce
• partial_sum
• exclusive_scan
• inclusive_scan
• transform_exclusive_scan
• transform_inclusive_scan
• adjacent_difference
• iota