What is "double dispatch"

n. (context computing English) A mechanism that dispatches a function call to different concrete functions depending on the runtime data types of two objects involved.

In software engineering, double dispatch is a special form of multiple dispatch, and a mechanism that dispatches a function call to different concrete functions depending on the runtime types of two objects involved in the call. In most object-oriented systems, the concrete function that is called from a function call in the code depends on the dynamic type of a single object and therefore they are known as single dispatch calls, or simply virtual function calls.