Re: advice on package design

[Martin Dowie <martin.dowie@btopenworld.com>]

Robert A Duff wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
> 
>>On 17 Mar 2005 09:04:26 -0500, Robert A Duff wrote:
>>
>>
>>>"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>
>>>>I agree with the idea, but I think that hiding should appear in a
>>>>declarative part. Less probably it should also qualify the thing being
>>>>hidden (like renames does):
>>>
>>>I don't believe in declarative parts.  I think declare/begin/end
>>>should not be required just because I want to declare a constant
>>>or something.
>>
>>Disagree. I don't like the idea of something changing its meaning within
>>the same scope, even if that is non-existing -> exiting. I have to tolerate
>>this in a declarative region because probably there is no better way to do
>>it. But I don't want to let it leak out of the quarantine zone.
> 
> 
> I don't understand what you mean about "changing meaning".
> I just want to be able to write things like:
> 
>     for I in A'Range loop
>         This_Component: constant T := A(I);
>         ... several uses of This_Component
>     end loop;
> 
> without adding three extra (useless) lines of code.
> And we agreed that if there's another thing called This_Component,
> this This_Component should not hide that This_Component.
> 
> The "hide" command I proposed is of dubious value, but if it were
> allowed, I wouldn't mind restricting it to whole procedures
> or something.  Or not.  But either way, I don't like the separation
> of "declarations" and "statements".

The bit about declarations and statements I don't like is where 
exceptions occur...

e.g.

with Ada.Text_IO; use Ada.Text_IO;
procedure Main is
    function Foo (I : Integer) return Integer is
       I2 : Integer := I + 1;
    begin
       return I2;
    exception
       when others =>
          return 0;
    end Foo;

    procedure Bar is
       I : Integer;
    begin
       I := Foo (Integer'Last);
    end Bar;
begin
    Bar;
exception
    when others =>
       Put_Line ("Rats... why not catch it in 'Foo'?");
end Main;

I've never understood why this needs to be this way...

Cheers

-- Martin