Hi All,

Quoting the original paper’s description for deduction guides for std::inplace_vector: "Unlike the other containers, inplace_vector does not have any deduction guides because there is no case in which it would be possible to deduce the second template argument, the capacity, from the initializer."

However, I found that in some cases it is possible to enable CTAD for std::inplace_vector, for example when we accept a std::array or std::span:

  template<class T, size_t N>

inplace_vector(from_range_t, const std::array<T, N>&) -> inplace_vector<T, N>; // new CTAD
Then we can:

  std::inplace_vector v{std::from_range, std::array{1, 2, 3}};

I think this makes meta-programming more user-friendly and convenient, for example, converting index_sequence into inplace_vector and then applying the algorithm in <algorithm>:

   constexpr inplace_vector v = []<size_t... Is>(index_sequence<Is...>) {    inplace_vector v{from_range, array{Is...}};
    auto [begin, end] = ranges::remove(v, 42);
    v.erase(begin, end);
    return v;
  }(std::make_index_sequence<N>{});

Would it be valuable for inplace_vector to introduce std::array or std::span-specific CTADs?

Thanks,
Hewill