How to use generics
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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.
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.
