Virtual function

Inheritable and overridable function or method for which dynamic dispatch is facilitated

Virtual functions are resolved 'late'. If the function in question is 'virtual' in the base class, the most-derived class's implementation of the function is called according to the actual type of the object referred to, regardless of the declared type of the pointer or reference. If it is not 'virtual', the method is resolved 'early' and selected according to the declared type of the pointer or reference.

In C, the mechanism behind virtual functions could be provided in the following manner:

Object-oriented languages typically manage memory allocation and de-allocation automatically when objects are created and destroyed. However, some object-oriented languages allow a custom destructor method to be implemented, if desired. If the language in question uses automatic memory management, the custom destructor (generally called a finalizer in this context) that is called is certain to be the appropriate one for the object in question. For example, if an object of type Wolf that inherits Animal is created, and both have custom destructors, the one called will be the one declared in Wolf.

In manual memory management contexts, the situation can be more complex, particularly in relation to static dispatch. If an object of type Wolf is created but pointed to by an Animal pointer, and it is this Animal pointer type that is deleted, the destructor called may actually be the one defined for Animal and not the one for Wolf, unless the destructor is virtual. This is particularly the case with C++, where the behavior is a common source of programming errors if destructors are not virtual.