Typekontroll

Typekontroll, or type checking, is the process of verifying and enforcing correct use of data types in programming languages. It aims to ensure that values are used in ways that conform to their declared or inferred types, preventing operations that would be semantically invalid, such as adding a number to a string.

Static type checking occurs at compile time. The compiler verifies types before the program runs, catching many errors early and potentially enabling optimizations. Static type systems often require explicit type annotations or use type inference to deduce types. Languages with static typing include Java, Rust, and Haskell, though some also support type inference to reduce boilerplate.

Dynamic type checking happens at run time. Types are checked as the program executes, which provides flexibility and can reduce upfront verbosity but may incur runtime overhead and lead to type errors only when the corresponding code path is executed. Languages such as Python and JavaScript are dynamically typed.

Many languages blend approaches in what is called gradual typing or hybrid type systems. These systems allow parts of a program to be statically typed while other parts remain dynamically typed, with type information flowing between regions. Type inference, generics, and polymorphism are common features that influence how strictly a language enforces types and how much boilerplate is required.

Key concepts in type systems include type safety, structural versus nominal typing, and strong versus weak typing. Type safety aims to prevent certain classes of runtime errors, while the exact guarantees depend on the language design. While type checking reduces a range of errors and can aid optimization and maintenance, it does not eliminate all runtime problems and may introduce complexity or verbosity in code.