[fpc-devel] Templates / Generics Syntax

[Mattias Gaertner]

On Thu, 3 Nov 2005 19:59:40 +0100 (CET)
Daniël Mantione <daniel.mantione at freepascal.org> wrote:

> 
> 
> Op Thu, 3 Nov 2005, schreef Mattias Gaertner:
> 
> > 
> > Here is a proposal of the syntax:
> > 
> > type
> >   TGenericClass<T,F> = class
> >   public
> >     procedure Add(Item: T; Flag: F);
> >   end;
> 
> This syntax is almost impossible to implement since in one of your other 
> mails the symbols to mark the parameters appear in regular source code:
> 
> begin
>   generictypeA<integer>.create
> end.
> 
> It will be very hard for the parser to see the difference in advance 
> between:
> 
>   variable<integer(another_var)
>   generic_type<integer
> 
> Only when the > symbol is parsed the result is known.
> 
> Maybe the parser may be able lookup the type first and make a decision 
> based on that, but it would be in the middle of a recursive expression 
> parse designed for infix operators.
> 
> Also in C++ this sometimes causes trouble where you need to change your 
> code notation so the compiler eats it. I don't know if this proposal 
> suffers from this mess, but we should avoid at all cost to import it into 
> Pascal.

Right. I didn't think of that.

What about edged brackets?

type
  TGenericClass[T,F] = class
  public
    procedure Add(Item: T; Flag: F);
  end;

procedure TGenericClass.Add(Item: T; Flag: F);
// Note: No redundant [T,F] after TGenericClass.
begin
end;

type TListOfComponent = TGenericList[TComponent];

Analog:
type TGenericListClass[T] = class of TGenericList[T];
type PGenericRecord[T] = ^TGenericRecord[T];

procedure GenericProc[T](Param: T);
begin
end;



Mattias