Polymorphism (computer science): Difference between revisions

Revision as of 15:42, 5 December 2023

Revision as of 15:02, 10 January 2024

Line 20:

===Ad hoc polymorphism===

{{main|Ad hoc polymorphism}}

[[Christopher Strachey]] chose the term ''ad hoc polymorphism'' to refer to polymorphic functions that can be applied to arguments of different types, but that behave differently depending on the type of the argument to which they are applied (also known as [[function overloading]] or [[operator overloading]]).<ref name=Strachey00/> The term "[[ad hoc]]" in this context is not intended to be pejorative; it refers simply to the fact that this form of polymorphism is not a fundamental feature of the type system. In the [[PascalJava (programming language)|Pascal]] / [[Delphi (programming language)|DelphiJava]] example below, the <code>Add</code> functions seem to work generically over two types (integer and string) when looking at the invocations, but are considered to be two entirely distinct functions by the compiler for all intents and purposes:

<syntaxhighlight lang="PascalJava">

class AdHocPolymorphic {

program Adhoc;

public String add(int x, int y) {

return "Sum: "+(x+y);

}

public String add(String name) {

function Add(x, y : Integer) : Integer;

return "Added "+name;

begin

Add := x + y}

}

end;

public class adhoc {

function Add(s, t : String) : String;

public static void main(String[] args) {

begin

AdHocPolymorphic poly = new AdHocPolymorphic();

Add := Concat(s, t)

end;

System.out.println( poly.add(1,2) ); // prints "Sum: 3"

begin

System.out.println( poly.add("Jay") ); // prints "Added Jay"

Writeln(Add(1, 2)); (* Prints "3" *)

}

Writeln(Add('Hello, ', 'Mammals!')); (* Prints "Hello, Mammals!" *)

}

end.

</syntaxhighlight>