Where contiguous storage is unnecessary, deque can be used as an alternative to vector in C++. This usage is employed by a large amount of code. However, vector supports reserve while deque does not, which forces users and library authors to determine this property on their own using SFINAE or requires expressions. I performed an exact search on GitHub using regular expressions, and this pattern appeared 483 times(https://github.com/search?q=%2Fif%5Cs%2Bconstexpr%5Cs*%5C%28%5B%5E%29%5D*reserve%5B%5E%29%5D*%5C%29%2F&type=code); the vast majority of them use requires expressions, and these code snippets represent the needs of the most advanced C++ users. Martin Leitner-Ankerl's well-known library unordered_dense also does this and supports C++17 (https://github.com/martinus/unordered_dense/blob/e5b9441ecf193f3e1e8f954527fc76edee20d7eb/include/ankerl/unordered_dense.h#L2094). I believe the C++ standard library needs to provide this functionality to prevent users from reinventing it themselves.

Reference implementation:

template<class C>
    requires (!std::ranges::view<C>) && std::ranges::sized_range<C>
constexpr void to(C c, std::ranges::range_size_t<C> n)
{
    if constexpr (requires { c.reserve(n); }) {
        c.reserve(n);
    }
}