constinit
constinit is a C++20 keyword used to specify that a variable with static or thread storage duration must be initialized at compile-time, ensuring constant initialization. It guarantees that the variable's initialization occurs during the static initialization phase, preventing runtime overhead and potential order-of-initialization issues. This is particularly useful for global or static variables where deterministic, zero-cost initialization is required.
Developers should use constinit when they need to enforce compile-time initialization for static or thread-local variables to avoid dynamic initialization costs and ensure predictable behavior in performance-critical or safety-critical systems. It is essential in scenarios like embedded systems, real-time applications, or when initializing global constants with complex expressions that can be evaluated at compile-time, such as in template metaprogramming or constexpr contexts.