Re: Reconsidering assignment

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 7 Cze, 00:52, Ray Blaak <rAYbl...@STRIPCAPStelus.net> wrote:

> > procedure To_Upper(S : in out String);
>
> > Such a procedure is perfectly reasonable.
> > What is not reasonable is this:
>
> > procedure Swap(X, Y : in out String);
>
> I don't see the difference. Consider:
>
>   declare
>     s : String := "123";
>   begin
>     To_Upper(s);
>   end;
>
>   procedure To_Upper(S : in out String)
>   begin
>     s := "12345678";
>   end;

Good point, but the solution is simple: ban it. :-)
You can ban it on the basis that the modifying operation (the s :=
"12345678") operates in (ie. potentially modifies) the constraint-
space in the context where the constraint itself is statically
unknown.

This is OK:

procedure To_Upper(S : in out String) is
begin
  for I in S'First .. S'Last loop
    S(I) := ...;
  end loop;
end;

Above none of the modifying operation (well, there is only one)
operates in the constraint-space of S.

> > procedure Safe_Swap(X, Y : in out String) with X'Length = Y'Length;
>
> Ugh. This is tedious. Seems easier to me to just let the contraint error happen.

The whole Ada is tedious. Let's move to Python, where even the chore
of writing begin/end is eliminated. ;-)


> If you really need this, also have a way to just say "with matching
> constraints" directly, e.g.
>
>   with X'Subtype = Y'Subtype
>
> That way one does not have to get all explicit for other types that have many
> explicit constraints.

Yes, that makes sense.

--
Maciej Sobczak
http://www.msobczak.com/