How will C++20 constexpr containers work?

Question

As constexpr std::string and constexpr std::vector have been accepted into C++20, how will these be used? The linked papers are very short on details. Do we need to specify

Answer 1

Those two papers depend heavily on P0784, which discusses how allocations at compile-time will work.

Incomplete answer:

• Only std::allocator will work.
• All allocations are tracked, and must be deallocated before compilation is complete. This means that you can do manipulations at compile-time, but you can't initialize string and vector variables to be used at run-time. (Personally, I think there's a good chance that this restriction will be lifted in a future version of the standard - but that's just my opinion.)