The Boost.Function library contains a family of class templates that are function object wrappers. The notion is similar to a generalized callback. It shares features with function pointers in that both define a call interface (e.g., a function taking two integer arguments and returning a floating-point value) through which some implementation can be called, and the implementation that is invoked may change throughout the course of the program.

Generally, any place in which a function pointer would be used to defer a call or make a callback, Boost.Function can be used instead to allow the user greater flexibility in the implementation of the target. Targets can be any 'compatible' function object (or function pointer), meaning that the arguments to the interface designated by Boost.Function can be converted to the arguments of the target function object.