[fpc-devel] Templates / Generics Syntax

[Mattias Gaertner]

On Fri, 04 Nov 2005 13:44:55 +0100
Marc Weustink <marc.weustink at cuperus.nl> wrote:

> Mattias Gaertner wrote:
> > On Fri, 04 Nov 2005 10:47:42 +0100
> > Marc Weustink <marc.weustink at cuperus.nl> wrote:
> > 
> > 
> >>Daniël Mantione 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.
> >>
> >>On the wiki pages some of my remarks got lost (or I didn't write them 
> >>down) but when I first looked at the <> notation style it looks very 
> >>unpascalish for me. I like more to add a new keyword for it, like the 
> >>samples wiht generic or template)
> >>
> >>BTW,
> >>what woud be the problem with
> >>
> >>type
> >>   TMySpecificClass = TGenericClass(TObject, Integer);
> > 
> > 
> > What about proc generics:
> > 
> > GenericProc(TObject)
> > 
> > This can be ambigious.
> 
> How would you have declared the proc, and how do you call it. I don't 
> see a problem yet.
> 
> GenericProc(TObject)(some params) you mean ?

Example:

procedure MyProc(T); // generic procedure without parameters
ver i: T;
begin
  ...
end;

procedure MyProc(T: TClass); // non generic procedure
begin
end;

Call

MyProc(TObject);

What will happen?

Mattias