constexpr Functions & Variables

constexpr on a function tells the compiler that the function can run during compilation when its arguments are themselves compile-time constants. That is a different feature from constexpr on a variable, which the Constants & Literals lesson covered briefly. This lesson goes deep on constexpr functions: how they evolved from a single-line trick in C++11 into a real subset of the language that can allocate memory in C++20, and when the keyword actually buys you compile-time evaluation versus when it sits there decorating the source.