How is C++20's std::vector assign constexpr?

Question

Given that the current contents and size of a vector can be randomly determined at runtime, and all contents will have to be destroyed upon calling assign, how can C++20's assign member function be constexpr ie. compile-time?

Answer 1

Found my answer here . To quote,

Being a constexpr function does not mean that the function is executed at compile time. It says, that the function has the potential to run at compile time. A constexpr function can also run a runtime. It's often a question of the compiler and the optimisation level if a constexpr functions runs at compile time or runtime.

Ergo, unlike constexpr variables, which must be determinable at compile time, one call of a given constexpr function may run at compile time, dependent on circumstance of calling (eg. a constexpr std::vector) and another at runtime (eg. a non-constexpr std::vector).