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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Expectation of Access Value Equality
Date: 05 Sep 2003 20:35:06 +0100
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Date: 2003-09-05T20:35:06+01:00
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"Nick Roberts" <nickroberts@blueyonder.co.uk> writes:

> I'm asking for the help of Ada programmers of all levels of experience.
> 
> Given the following declarations:
> 
>    type A_String is access constant String;
> 
>    function "+" (S: String) return A_String is
>    begin
>       return new String'(S);
>    end;
> 
>    type A_String_Array is array (Positive range <>) of String;
> 
>    procedure Print (A: in A_String_Array) is
>       Sentinel: constant A_String := A(A'Last);
>       Current: Positive := A'First;
>    begin
>       loop
>          Put_Line( A(Current).all );
>          exit when A(Current) = Sentinel;
>          Current := Current + 1;
>       end loop;
>    end;

That is a pretty bizarre piece of code! (E&OE). I guess there might be
circumstances in which the part at issue was the right thing to do ..

> (a) Would you be surprised by:
> 
>    Print( (+"foo",+"bar",+"",+"") );
>
> printing three lines?

yes

> (b) Would you be surprised by:
> 
>    Print( (+"foo",+"bar",+"hum",+"foo") );
> 
> printing one line?

yes

> (c) What would you think of an implementation that caused this behaviour?
> (What would you think of an implementation that printed four lines in both
> cases?)

odd, needs study
(ok)

> (d) I'd be grateful for a very brief indication of your level and broad
> area(s) of programming experience, in Ada and other languages.

expert user, not language lawyer
would be surprised by the same behaviours in C
otherwise tend to use scripting languages so question doesn't arise


If an amended ARM said the surprising behaviours were OK I would not
be concerned, plenty of other implementation-defined stuff to avoid in
the language!