constexpr

`constexpr` is a feature in programming languages like C++ that allows developers to tell the compiler certain values or functions should be calculated at compile time, rather than during program execution. This enables the creation of constants and functions that can be evaluated before the program runs, leading to faster, more efficient code. Think of it as marking certain calculations as "done ahead of time," so the program doesn't spend time recomputing them when it runs. It's useful for optimizing performance and ensuring values remain fixed during execution.