From: Victor Porton <porton@narod.ru>
Subject: Re: A good program that not compile
Date: Wed, 21 May 2014 17:10:14 +0300
Date: 2014-05-21T17:10:14+03:00 [thread overview]
Message-ID: <llic43$kge$1@speranza.aioe.org> (raw)
In-Reply-To: lyk39f6y39.fsf@pushface.org
Simon Wright wrote:
> Victor Porton <porton@narod.ru> writes:
>
>> The following does not compile.
>
> For very good reasons.
>
> Obtain_Handle(File_Handle) ought to be a function!
> It should take an in parameter, not in out!
>
> I take it your point is that you want to be able to declare
>
> function Obtain_Handle(Object: Abstract_Handle) return Integer
> is abstract;
>
> but I find that (with the latest compilers) this works:
>
> function Obtain_Handle(Object: Abstract_Handle) return Integer
> is (raise Program_Error);
>
> with the slight disadvantage of postponing failure to run time (which
> might happen anyway with your proposal).
I have rewritten it with your suggestions. Now it does compile, but instead
as of to work as intended (Assigning 123 to the Handle) it raises
Program_Error.
Can we save my program and make it work as intended?
The listing follows:
-- my.ads
with Ada.Finalization;
package My is
type Abstract_Handle is new Ada.Finalization.Limited_Controlled with
record
Handle: Integer;
end record;
function Obtain_Handle(Object: Abstract_Handle) return Integer;
overriding procedure Initialize(Object: in out Abstract_Handle);
type File_Handle is new Abstract_Handle with null record;
overriding function Obtain_Handle(Object: File_Handle) return Integer;
end My;
-- my.adb
package body My is
function Obtain_Handle(Object: Abstract_Handle) return Integer is
begin
raise Program_Error;
return 0;
end;
overriding procedure Initialize(Object: in out Abstract_Handle) is
begin
Object.Handle := Obtain_Handle(Object);
end;
overriding function Obtain_Handle(Object: File_Handle) return Integer is
begin
return 123; -- Suppose 123 is a file handle, for an example
end;
end My;
-- main.adb
with My;
with Ada.Text_IO;
procedure Main is
X: My.File_Handle;
begin
Ada.Text_IO.Put_Line(Integer'Image(X.Handle));
end;
--
Victor Porton - http://portonvictor.org
next prev parent reply other threads:[~2014-05-21 14:10 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-21 13:05 A good program that not compile Victor Porton
2014-05-21 13:49 ` Simon Wright
2014-05-21 14:10 ` Victor Porton [this message]
2014-05-21 14:24 ` Victor Porton
2014-05-21 15:58 ` Simon Wright
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