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For example, to have a derived class with an overloaded function taking a double or an int, using the function taking an int from the base class, in C++, one would write: class B { public : void F ( int i ); }; class D : public B { public : using B :: F ; void F ( double d ); };
There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class. [9]
And even if methods owned by the base class call the virtual method, they will instead be calling the derived method. Overloading occurs when two or more methods in one class have the same method name but different parameters. Overriding means having two methods with the same method name and parameters. Overloading is also referred to as ...
Perhaps the most well-known example is C++, an object-oriented extension of the C programming language. Due to the design requirements to add the object-oriented paradigm on to an existing procedural language, message passing in C++ has some unique capabilities and terminologies. For example, in C++ a method is known as a member function.
The method signatures help distinguish overloaded methods (methods with the same name) in a class. Return types are not included in overloading. Only method signatures should be used to distinguish overloaded methods. [6] For example, the following two methods have different signatures:
The "vtable" method developed in C++ and other early OO languages (where each class has an array of function pointers corresponding to that class's virtual functions) is nearly as fast as a static method call, requiring O(1) overhead and only one additional memory lookup even in the un-optimized case. However, the vtable method uses the ...
The previous section notwithstanding, there are other ways in which ad hoc polymorphism can work out. Consider for example the Smalltalk language. In Smalltalk, the overloading is done at run time, as the methods ("function implementation") for each overloaded message ("overloaded function") are resolved when they are about to be executed.
Thus, there is no name collision, and no virtual table lookup. By contrast, dynamic dispatch is based on the type of the calling object, meaning it uses virtual functions (overriding) instead of function overloading, and does result in a vtable lookup. Consider the following example, written in C++, of collisions in a game: