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From: "Grein, Christoph" <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Generic default parameters
Date: Tue, 14 May 2002 13:03:46 +0200 (MET DST)
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Date: 2002-05-14T13:03:46+02:00

> >I do see problems with this proposal. First of all it would be a major 
upwardly 
> >incompatible change and break old code - a NONO for the ARG.
> ...
> True. It would make some old code ambiguous. However the ambiguity can
> be relatively easily resolved.

Easy or not, only if absolutely necessary would the ARG be willing to change the 
language in a way that is upwardly incompatible. This proposal does not seem 
worth it.

> >This being the case, it seems useless to discuss how matching rules for 
> >subprograms with defaulted parameters should be defined - they are not so 
> >obvious for me.
> 
> In fact I thought that the matching rules for subprogram renaming
> should be relaxed with regard of default values. Presently, generics
> just use that rules. I wished these rules were same as ones for
> subprogram calls. Maybe, as close as:
> 
>    function Int_Sqrt (X : Integer) renames Sqrt (Float (X));
>    procedure Debug (X : Integer)
>       renames Put_Line
>          (File=>My_File; Item=>Integer'Image (X));

This is invalid syntax (I can imagine what you mean - it's a mess). But the 
rules would not be so simple. Defaulted parameters need not come last (in this 
way you force named association when omitting parameters).

So would either subprogram

  procedure (X: S; Y: T := Def);
  procedure (X: T := Def; Y: S);

match

  procedure (W: S);

What about

  procedure (X: S; Y: S := Def);
  procedure (X: S := Def; Y: S);

Would they both match?