Re: Expectation of Access Value Equality

[amado.alves@netcabo.pt (Mário Amado Alves)]

"Nick Roberts" <nickroberts@blueyonder.co.uk> wrote in message news:<bja3fi$glkjh$1@ID-25716.news.uni-berlin.de>...
> 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 A_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;
> 
> (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?

I would think the behaviour was not in accordance with the deep,
natural meaning of "new". I would suspect the system was trying to
reuse memory, at the cost of some search time. And I would hope this
behaviour was a compiler option. And wish it was not the default.

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

All is well.

> (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.

I'm programming since 1984, in Ada since 1997, and before it was in
BASIC, Assembler, Clipper, QuickBASIC, Pascal, C, C++, Java... I'm an
academic now but I have worked for industry and sometimes I still do
freelance work.