Proceduretype

Proceduretype, also referred to as procedural type or function type, is a programming concept that represents the type of a subroutine or procedure. It encodes the signature of a callable: the parameters it accepts and, depending on the language, the return type and calling conventions. In languages that distinguish procedures from functions, a procedure type captures only the aspects needed to invoke the subroutine, while a function type includes a return value.

In practice, procedural types allow values that refer to procedures to be stored, passed as arguments, or returned from functions. This enables higher-order programming, callbacks, and event handling. Exact syntax and capabilities vary by language, but the core idea is language support for first-class procedures or function pointers.

Examples by language concept:

- Pascal/Delphi: procedural types can be declared to match a procedure signature, enabling variables to hold references to procedures and to invoke them later.

- C#: delegates act as procedural types, with predefined forms like Action and Func, enabling strong typing for method references.

- TypeScript: a type alias can describe a procedure signature, such as a function type that returns void, allowing variables to hold functions with a given parameter list.

- Other languages may use function pointers, interfaces, or lambda expressions to achieve similar functionality.

Common uses include callbacks for asynchronous operations, event handlers in user interfaces, and generic utilities that operate on any procedure matching a given signature. Limitations include language-specific rules on variance, generics, and closure capture, which affect how a procedure type can be used with different arguments or environments.

See also: function type, callback, delegate, higher-order function.