Adding namespace to avoid conflict with C++20 construct_at

[g-217]

With C++20 I was getting compilation errors because of ambiguity in selecting construct_at, construct_at is defined in both std & adobe namespace.

[sean-parent]

One change requested - the remaining changes look good.

[sean-parent]

I don't even know what I was thinking with this code -
Having the conditional in the header is asking for ODR violations. I would suggest starting at line [356-370] be replaced with:

template <class T, class... Args>
T* construct_at(T* p, Args&&... args) {
    return ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...);
}

From cppreference. The constexpr with the cast isn't doing anything, and I'm surprised it doesn't generate a warning. Clearly, the C++20 implementation never compiled; your suggestion loses the constexpr-ness of the standard call. Let's keep it simple and when we require C++20 we can deprecate this instance.

[g-217]

replaced the code between lines [356-370] with suggested implementation.

[sean-parent]

LGTM