Re: Language lawyer question: Equality on 'Access attributes

["Robert I. Eachus" <rieachus@comcast.net>]

Dmitry A. Kazakov wrote:

> Just summarizing...
> 
> Your point is that the compiler should consider all visible types and all
> visible "=" to crunch X'Access = Y'Access. Then X'Access = Y'Access is
> illegal if there is no visible named access types. Then provided:
> 
> type A is tagged null record;
> type A_Ptr is access all A;
> function "=" (Left : A_Ptr; Right : access A) return Boolean;
> X : aliased A;
> Y : aliased A;
> 
> X'Access = Y'Access -- is ambiguous

That I certainly agree with.  But there are two further issues that MAY 
apply in the actual example.  The first is that predefined operators 
don't need to be visible to be considered by overload resolution. 
(Usually there are other overload resolution rules that result in 
interpretations using invisible operators being eliminated.)  The second 
is that the rule that anonymous access types don't have a predefined "=" 
operator is not a syntax or overload resolution rule.

The combination of the above can result in an invisible anonymouns 
access Integer type creating an overload interpretation that is illegal 
rather than ignored.  If RM 4.5.2(6) should be considered as a 
overloading rule, that eliminates potential problems in the original 
case.  (However, the part of the 4.5.2(6) rule for limited types 
shouldn't become a name resolution rule.  The rules for re-emergence of 
predefined equality for limited types are somewhat confusing, but 
changing them might be worse.)

In any case, your example would still be illegal, since the user defined 
"=" is visible.

-- 
                                           Robert I. Eachus

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