Revision 1 of 1, by RogueScholar on 9-20-2023. The page as it is now.

How to use generics

An example of how to use generics to write a function gmax() that takes the maximum of two not-yet-typed variables. Note that while the functions here are namespaced by the classname, FPC versions from 3.1.1 onwards also support fully free-standing generic methods.

pascal

program UseGenerics;

{$mode objfpc}{$H+}

type
  generic TFakeClass<_GT> = class
    class function gmax(a,b: _GT):_GT;
  end;

  TFakeClassInt = specialize TFakeClass<integer>;
  TFakeClassDouble = specialize TFakeClass<double>;

  class function TFakeClass.gmax(a,b: _GT):_GT;
  begin
    if a > b then 
      result := a
    else 
      result := b;
  end;

begin
    // show max of two integers
  writeln( 'Integer GMax:', TFakeClassInt.gmax( 23, 56 ) );
    // show max of two doubles
  writeln( 'Double GMax:', TFakeClassDouble.gmax( 23.89, 56.5) );
  readln();
end.

From the Free Pascal wiki, page "How to use generics", as it stood on 2023-09-20 after a change by RogueScholar, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.