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Method overloading, on the other hand, refers to differentiating the code used to handle a message based on the parameters of the method. If one views the receiving object as the first parameter in any method then overriding is just a special case of overloading where the selection is based only on the first argument.
The functions must have different type signatures, i.e. differ in the number or the types of their formal parameters (as in C++) or additionally in their return type (as in Ada). [9] Function overloading is usually associated with statically-typed programming languages that enforce type checking in function calls. An overloaded function is a ...
When overriding one method with another, the signatures of the two methods must be identical (and with same visibility). In C#, class methods, indexers, properties and events can all be overridden. Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override.
The C++ examples in this section demonstrate the principle of using composition and interfaces to achieve code reuse and polymorphism. Due to the C++ language not having a dedicated keyword to declare interfaces, the following C++ example uses inheritance from a pure abstract base class.
In C++, the "base" function is called. Specifically, the most derived function that is not more derived than the current constructor or destructor's class is called. [7]: §15.7.3 [8] [9] If that function is a pure virtual function, then undefined behavior occurs.
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.
Multiple dispatch or multimethods is a feature of some programming languages in which a function or method can be dynamically dispatched based on the run-time (dynamic) type or, in the more general case, some other attribute of more than one of its arguments. [1]
For instance, in C#, the base method or property can only be overridden in a subclass if it is marked with the virtual, abstract, or override modifier, while in programming languages such as Java, different methods can be called to override other methods. [15] An alternative to overriding is hiding the inherited code.