Invokable

Invokable is an adjective describing something that can be invoked, called, or activated. In computing, an invokable object or function is one that can be executed or invoked like a function.

In programming languages, objects become invokable by implementing a special mechanism that enables a call operation. Python makes an object invokable by defining a __call__ method; calling the instance as obj(...) invokes __call__. PHP follows a similar idea with the __invoke magic method, allowing objects to behave like functions and enabling patterns such as invokable controllers in some frameworks. In C++, callable objects are achieved by defining operator() on a class, or by using the language’s standard concepts and type traits. Since C++20, the formal concept is often referred to as invocable (with an e) and is exposed through traits like std::is_invocable and the concept std::invocable to verify whether a type can be called with given arguments.

JavaScript treats functions as first-class citizens, and function values are inherently invokable. Making an arbitrary object invokable in JavaScript typically requires using a function or a proxy pattern rather than a built-in language feature for general object invocation.

The term is also used more broadly to describe interfaces, endpoints, or commands that can be summoned or executed, such as an API operation that can be invoked by a client.

Etymology traces to invoke, from Latin invocare, meaning to call upon. See also invocation, callable, __invoke, __call, operator().