Runtimechecked

Runtimechecked refers to the practice of performing validation and enforcement of constraints during program execution, rather than relying solely on static compile-time checks. In software development, runtime checks verify types, values, and invariants as a program runs, and can complement static analysis or dynamic typing. The approach is common in dynamically typed languages and in systems that support optional or gradual typing, where safety guarantees are desirable without sacrificing flexibility.

Common forms of runtime checking include assertions, precondition and postcondition checks (design by contract), runtime type checking, and enforcement of security or API contracts through wrappers or instrumentation. Tools and libraries implement these checks as runtime wrappers, decorators, or by instrumenting code paths. Some languages, such as Eiffel and D, include built-in support for run-time contracts with automatic checking; others rely on libraries or developer-implemented guard clauses.

Benefits of runtime checking include earlier error detection, improved fault localization, and stronger safety guarantees in edge cases or boundary conditions. Drawbacks include performance overhead, potential for overwhelming users with failures if checks are too aggressive, and possible duplication with static analysis. Design considerations involve selecting which invariants to enforce at runtime, how to report violations, and how to balance safety with performance.

Runtime checking is a key component of runtime verification, contract programming, and inter-language boundaries. It complements static type systems and formal verification by providing practical safety checks in production environments.

See also: runtime verification, contract programming, assertions, gradual typing.