In some programming languages, function overloading or method overloading is the ability to create multiple functions of the same name with different implementations. Calls to an overloaded function will run a specific implementation of that function appropriate to the context of the call, allowing one function call to perform different tasks depending on context.

For example, doTask() and doTask(object o) are overloaded functions. To call the latter, an object must be passed as a parameter, whereas the former does not require a parameter, and is called with an empty parameter field. A common error would be to assign a default value to the object in the second function, which would result in an ambiguous call error, as the compiler wouldn't know which of the two methods to use.

Another example is a Print(object o) function that executes different actions based on whether it's printing text or photos. The two different functions may be overloaded as Print(text_object T); Print(image_object P). If we write the overloaded print functions for all objects our program will "print", we never have to worry about the type of the object, and the correct function call again, the call is always: Print(something).

Languages which support function overloading include, but are not necessarily limited to, the following:

Languages that do not support function overloading include C, Python, Rust and Zig.

Function overloading is usually associated with statically-typed programming languages that enforce type checking in function calls. An overloaded function is a set of different functions that are callable with the same name. For any particular call, the compiler determines which overloaded function to use and resolves this at compile time. This is true for programming languages such as Java.

Function overloading differs from forms of polymorphism where the choice is made at runtime, e.g. through virtual functions, instead of statically.

Example: Function overloading in C++