为什么在C ++ 20中没有使std :: accumulate成为constexpr? [英] Why has std::accumulate not been made constexpr in C++20?

问题描述

在C ++ 20中，许多(大多数?)C ++标准库算法已被制成 constexpr .但是- std :: accumulate 还没有./p>

好像是，它可能是:

  template< class InputIt，class T>constexpr T累加(InputIt首先，InputIt最后，T init){for(; first！= last; ++ first){初始化= std :: move(init)+ * first;}返回init；} 

所以-是否有没有同样使用 constexpr 的原因?

注意:此问题是出于我的回答对解决方案

P1645R1 实际上是在贝尔法斯特会议上采用的响应NB评论 US 320 包含在C ++ 20中.

因此，以下所有算法将在C ++ 20中成为 constexpr (它们的重载除外，它们的重载采用 ExecutionPolicy ):

• 积累
• 减少
• 内部产品
• transform_reduce
• partial_sum
• exclusive_scan
• inclusive_scan
• transform_exclusive_scan
• transform_inclusive_scan
• adjacent_difference
• iota

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.

解决方案

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

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