Hello and welcome to C++ Insights. Today we’re unpacking Andreas Fertig’s article titled “constexpr Functions: Optimization vs Guarantee.” Fertig observes that many developers assume a constexpr function, once supplied with compile-time values, will be evaluated at compile time. But he warns, “What you get is not what you see.” Compiler optimizations—especially implicit inline—can produce the same assembly whether you declare a function constexpr or not. To obtain a true compile-time guarantee, you must force constant evaluation. Fertig outlines four techniques: assign the result to a constexpr variable, use it as a non-type template argument, as an array size, or inside another constexpr function. Only then does a misuse—such as dividing by zero—result in a compile-time error. “constexpr can give you more!” he says, providing an evaluation free of undefined behavior. Thanks for listening to C++ Insights.
Link to Article