Re: Ada2012 Invariants and obaque types

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Hi Martin,

Unless I've missed something, I do not see the point. Whether or not you  
use an invariant, if the public view assert the type is tagged, the full  
view must be tagged. This was the same, even prior to Ada 2012. Otherwise,  
how would you derive from a tagged public view and define class wide view,  
 from a type whose private view isn't tagged ?

Just out of curiosity: which GNAT flavor do you use for Ada 2012 ?

Le Tue, 21 Jun 2011 10:53:31 +0200, Martin <martin.dowie@btopenworld.com>  
a écrit:

> A fairly common Ada idiom is to define the full view of a private type
> using an incomplete declaration. Thus leaving the actual
> implementation to the package spec. Trying this out with the public
> view defined with an invariant lead to a compiler error - is this:
>
> a) expected?
> b) an unexpected consequence? or
> c) a compiler bug?
>
> Example:
> package P1 is
>    type T1 is tagged private
>       with Invariant => Is_Valid (T1);
>    function Create               return T1;
>    function Is_Valid (This : T1) return Boolean;
> private
>    type Imp;
>    type T1 is
>       record
>          I : Imp;
>       end record;
> end P1;
>
> gnatmake -ws -c -u -PH:\Ada\test_invariants\test_invariants.gpr p1.ads
> gcc -c -g -g -gnatE -gnatVn -gnato -fstack-check -gnat12 -gnatf -I- -
> gnatA H:\Ada\test_invariants\src\p1.ads
> p1.ads:11:04: type "Imp" is frozen at line 3 before its full
> declaration
> p1.ads:13:09: full declaration of private type "T1" defined at line 3
> must be a tagged type
> p1.ads:15:14: invalid use of type before its full declaration
> gnatmake: "H:\Ada\test_invariants\src\p1.ads" compilation error
>
> [2011-06-21 09:46:55] process exited with status 4 (elapsed time:
> 00.26s)


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