Hi All,

Quoting the original paper’s description
<https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p0843r14.html#Deduction-guides>
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