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From: AdaMagica <christ-usch.grein@t-online.de>
Newsgroups: comp.lang.ada
Subject: Re: A hole in Ada type safety
Date: Thu, 12 May 2011 22:31:17 -0700 (PDT)
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Date: 2011-05-12T22:31:17-07:00
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On 13 Mai, 02:47, a...@att.net wrote:
> --
> -- =A0May be this program will help explain the problem.
> --

(erased a lot of irrelevant stuff)

> =A0 -- ------------------ --
> =A0 -- =A0Ada05_Conversion =A0--
> =A0 -- ------------------ --
> =A0 generic
> =A0 =A0 type Source (<>) is limited private ;
> =A0 =A0 type Target (<>) is limited private ;
> =A0 =A0 function Ada05_Conversion ( S : Source ) return Target ;
>
> =A0 function Ada05_Conversion ( S : Source ) return Target is
>
> =A0 =A0 =A0 pragma Suppress ( All_Checks ) ;
>
> =A0 =A0 begin
> =A0 =A0 =A0 -- Compiling Error messages:
> =A0 =A0 =A0 -- =A0 (Ada 2005) cannot copy object of a limited type
> =A0 =A0 =A0 -- =A0 =A0 =A0 =A0 =A0 =A0 =A0(RM-2005 6.5(5.5/2))
> =A0 =A0 =A0 -- =A0 consider switching to return of access type
> =A0 =A0 =A0 --
> =A0 =A0 =A0 -- Additional References for reasoning:
> =A0 =A0 =A0 -- =A0 RM 7.5 Limited Types ( 1/2, 1.a, 1.b/2 )
> =A0 =A0 =A0 --
> =A0 =A0 =A0 return Target ( S ) ;

What you are writing here is a normal type conversion with certain
rules (RM 4.6), not an unchecked type conversion (RM 13.9). For a type
conversion to be legal, the types involved have to be convertible.
Source and Target are not convertible, so this whole thing is illegal
for several reasons.

> =A0 =A0 end Ada05_Conversion ;

RTFM