Editing Ad hoc polymorphism (section)

==Early binding==
Ad hoc polymorphism is a [[dynamic dispatch|dispatch]] mechanism: control moving through one named function is dispatched to various other functions without having to specify the exact function being called. Overloading allows multiple functions taking different types to be defined with the same name; the [[compiler]] or [[interpreter (computing)|interpreter]] automatically ensures that the right function is called. This way, functions appending lists of [[integer]]s, lists of [[string (computer science)|string]]s, lists of [[real number]]s, and so on could be written, and all be called ''append''&mdash;and the right ''append'' function would be called based on the type of lists being appended. This differs from parametric polymorphism, in which the function would need to be written ''generically'', to work with any kind of list. Using overloading, it is possible to have a function perform two completely different things based on the type of input passed to it; this is not possible with parametric polymorphism (but would have to be achieved with switching on the type inside the generic function). Another way to look at overloading is that a routine is uniquely identified not by its name, but by the combination of its name and the number, order and types of its parameters.

This type of polymorphism is common in [[object-oriented programming]] languages, many of which allow [[operator (programming)|operator]]s to be overloaded in a manner similar to functions (see [[operator overloading]]). Some languages that are not dynamically typed and lack ad hoc  polymorphism (including type classes) have longer function names such as <code>print_int</code>, <code>print_string</code>, etc. This can be seen as advantage (more descriptive) or a disadvantage (overly verbose) depending on one's point of view.

An advantage that is sometimes gained from overloading is the appearance of specialization, e.g., a function with the same name can be implemented in multiple different ways, each optimized for the particular data types that it operates on. This can provide a convenient interface for code that needs to be specialized to multiple situations for performance reasons. The downside is that the type system cannot guarantee the consistency of the different implementations.

Since overloading is done at compile time, it is not a substitute for [[late binding]] as found in [[subtyping polymorphism]].