CompileTimeChecks

CompileTimeChecks refers to techniques for verifying properties of code during compilation rather than at runtime. By performing checks at compile time, programs can fail early, invariants can be enforced, and potentially more optimized code paths can be selected. Compile-time checks are supported by language type systems, compilers, and language features that can compute or reason about values without executing the program.

Common mechanisms include static assertions (for example, C++ static_assert(sizeof(int) == 4, 'int size must be 4')), compile-time evaluation (constexpr or consteval in C++, or equivalent features in other languages), and constraints on generics or templates (C++ concepts, Rust trait bounds) that require certain interfaces or properties. SFINAE and type traits are used to select overloads or branches based on type properties. Some languages provide compile-time reflection or comptime features to generate code conditioned on compile-time values.

In practice, compile-time checks help catch misuse, enforce invariants, and enable specialized implementations. They can also yield more optimized code by removing runtime branches. However, they can increase code complexity, extend compile times, and may obscure runtime behavior if overused. They are not a substitute for runtime validation of external inputs or dynamic conditions.

Examples by language include C++ static_assert and concepts; Rust's trait bounds and const generics; D's static if and static assert; Zig's comptime. See also static type checking, static_assert, constexpr, templates, and compile-time evaluation.