[fpc-pascal] Implicit generic specializations

[Ryan Joseph]

Since I had was already working on generics I wanted to see if I could implement the inferred specializations like is available in Delphi. The current syntax is too verbose to be usable so this is a necessary improvement in my opinion.

Here’s a first draft which seems to be working. There’s probably other ways to do the inference (I don’t have Delphi to test there’s) but this what I did for now. The algorithm basically scans params in order of appearance and inserts unique non-repeating types. For example:

            (1,'string') = <Integer,String>
            (1,2,3,4,5,6) = <Integer>
            ('a','b') = <String>
            ('string',1) = <String,Integer>
            ('a',1,'b',2,'c') = <String,Integer>


https://github.com/genericptr/freepascal/tree/generic_implicit


{$mode objfpc}
{$modeswitch implicitgenerics}

program test;

generic procedure DoThis<T>(msg:T);
begin
	writeln('DoThis$1#1:',msg);
end;

generic procedure DoThis<T>(msg:T;param1:T);
begin
	writeln('DoThis$1#2:',msg,' ',param1);
end;

generic procedure DoThis<T,U>(msg:T);
begin
	writeln('DoThis$2#1:',msg);
end;

generic procedure DoThis<T,U>(msg:T;param1:U);
begin
	writeln('DoThis$2#2:',msg,' ',param1);
end;

generic procedure DoThis<T,U>(msg:T;param1:U;param2:tobject);
begin
	writeln('DoThis$2#3:',msg,' ',param1,' ',param2.classname);
end;

begin
	DoThis(1);			// DoThis$1#1:1
	DoThis(1,1);			// DoThis$1#2:1 1
	DoThis('a','a');		// DoThis$1#2:a a
	DoThis('a',1);			// DoThis$2#2:a 1
	DoThis('a',1,tobject.create);	// DoThis$2#3:a 1 TObject
end.

Regards,
	Ryan Joseph