RunTimeChecks

Runtime checks are validations performed during program execution to verify that assumptions about data, state, or operations hold true. They complement compile-time type checking and static analysis by catching errors that slip through earlier stages, helping detect issues such as invalid inputs, illegal state, or contract violations.

Common forms of runtime checks include bounds checks on array or collection indices, null or undefined reference checks, type checks in dynamically typed languages, range and overflow checks for arithmetic, and invariant or contract checks that enforce preconditions and postconditions. Runtime checks may also cover security constraints, resource limits, and error handling pathways.

Implementation techniques vary. They include assertions that halt execution when a condition fails, runtime libraries or language features that enforce contracts, and instrumentation of code or virtual machines to monitor behavior. Some checks are always active, while others are optional or can be enabled or disabled, for example in debugging versus production builds.

Advantages of runtime checks include early error detection, clearer diagnostics, and enhanced safety and robustness in environments with weaker static guarantees. They are also central to design by contract and API reliability. On the downside, runtime checks introduce performance overhead, increase code size, and can complicate release builds if assertions or checks are disabled or removed.

Contexts and language impact vary: dynamic languages such as Python or JavaScript rely heavily on runtime validation, while statically typed languages still perform runtime checks for casts, reflection, or interface dispatch. Runtime checks are a common tool for improving correctness and security across software systems.