[fpc-devel] Templates / Generics

[dannym]

Hi,

Am Freitag, den 04.11.2005, 19:33 +0100 schrieb Peter Vreman:
> At 18:17 4-11-2005, you wrote:
> >This is evaluated by the pre-compiler run during compile time.
> >
> >When you use the template with e.g.
> >var
> >bl: List<String>;
> >
> >then procedure show(s:string) is taken.
> >
> 
> But what if the bl: List<String> is called from an other unit? The 
> Show(string) is then not visible anymore?

Put the Show(string) into the ppu too, with a mangled name, and save any
calls of Show within the generic type implementation to the ppu, writing
the mangled name. 

Excuse the stupid made-up example below, but I can't think of anything
that really _needs_ global functions right now, so I cheated by using
class functions and a global catch-all variable to require a global
translation function:

unit ubaz;

interface

type
  TCache = generic(T: TObject) class(TObject)
  published
    class procedure Put(Name: string; Instance: T);
    class function Get(Name: string): T;
  end;

implementation

var
  gCachedObjects: array of TObject; 
  gCachedNames: array of string;

function FooToBar(Name: string; Instance: TObject): string;
begin
  Result := T.ClassName + '_' + Name;
end;

class procedure TCache.Put(Name: string; Instance: T);
begin
  SetLength(gCachedObjects, Length(gCachedObjects) + 1);
  SetLength(gCachedNames, Length(gCachedNames) + 1);
  gCachedObjects[High(gCachedObjects)] := Instance;
  gCachedNames[High(gCachedNames)] := FooToBar(Name, Instance);
end;

class function TCache.Get(Name: string): T;
var
  i: Integer;
begin
  Result := nil;
  for i := 0 to High(gCachedNames) do begin
    if gCachedNames[i] = Name then begin
      if gCachedObjects[i] is T then begin
        Result := gCachedObjects[i];
      end;
      Break;
    end;
  end;  
end;

end.

the generated ppu should have

  $Private$FooToBar$string$TObject: function ($2843423)

  and the generic parts:
    ....
    gCachedNames[High(gCachedNames)] := uBaz.$Private$FooToBar(Name,
Instance);
    
Or did I miss something important ? (apart from the act of
auto-publishing of the function although it is not in the interface
section being a bit evil)

cheers,
   Danny

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