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c++stdvectorc++20constexpr

Why is std::vector::push_back declared as constexpr in C++20?

According to cppref, in C++20, std::vector::push_back is declared as follows:

constexpr void push_back(const T& value);

I cannot imagine a scenario in which push_back should be constexpr.

What's the rationale behind?

Solution

  • Is there any rationale behind?

    This is the abstract of the proposal. There is no separate rationale section:

    P1004R2 Making std::vector constexpr

    Abstract

    std::vector is not currently constexpr friendly. With the loosening of requirements on constexpr in [P0784R1] and related papers, we can now make std::vector constexpr, and we should in order to support the constexpr reflection effort (and other evident use cases).