Re: Expectation of Access Value Equality

[Jeffrey Carter <spam@spam.com>]

Nick Roberts wrote:

> 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;

Later corrected this line with:

> I'm sorry, I did mean:
> 
>    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;

My reaction is to wonder why you're not using a for loop here:

for Current in A'range loop

If you can come up with a real example where this is relevant, it would 
make the answers of greater interest.

At first glance, I'd expect both examples to print 4 lines. If an 
implementation didn't give that behavior, though, I suspect I'd look 
further at the fact that you're using "access constant", so the compiler 
could save only a single copy of the duplicated values, and use the same 
access value for equal strings. Both results (4 lines or fewer than 4 
lines) seem legal.

> (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've been using Ada since 1984; I'm not a language lawyer or compiler 
writer, but I think I have a pretty good understanding of the language. 
I've also used a number of other languages, including BASICs, Pascals, 
FORTRAN-66, COBOL, C, and assemblers.

-- 
Jeff Carter
"You couldn't catch clap in a brothel, silly English K...niggets."
Monty Python & the Holy Grail
19