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From: Blady <p.p11@orange.fr>
Newsgroups: comp.lang.ada
Subject: Re: Equivalence between named access and anonymous access.
Date: Thu, 7 Sep 2023 18:06:15 +0200
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Le 06/09/2023 à 17:54, Dmitry A. Kazakov a écrit :
> On 2023-09-06 16:37, Blady wrote:
> 
>> I'm wondering about named access and anonymous access.
>> In the following Ada code, are the writing of parameter P1 type of 
>> procedures PA and PB equivalent ?
>>
>> package C1 is
>>    type Inst is tagged null record;
>>    type Class is access all Inst'Class;
>> end C1;
>>
>> with C1;
>> package C2 is
>>    type Inst is tagged null record;
>>    type Class is access all Inst'Class;
>>
>>    procedure PA (Self : Inst; P1 : C1.Class); -- named access
>>    procedure PB (Self : Inst; P1 : access C1.Inst'Class); -- anonymous 
>> access
>> end C2;
>>
>> Same with:
>>    function FA (Self : Inst) return C1.Class; -- named access
>>    function FB (Self : Inst) return access C1.Inst'Class; -- anonymous 
>> access
>>
>> Are FA and FB writing equivalent?
>> If not why?
> 
> They are not equivalent from the access checks point of view:
> 
>     declare
>        Y : C2.Inst;
>        X : aliased C1.Inst;
>     begin
>        C2.PA (Y, X'Access); -- Non-local pointer error
>        C2.PB (Y, X'Access); -- Fine
>     end;
> 
> Furthermore, tagged anonymous access is controlling (dispatches) when 
> not class-wide.
> 

Thanks Dmitry, also Gautier and Jeff for your previous answers,

Well, I was questioning myself about the choice between named access and 
anonymous access in the old Ada port of Java library, for instance:

    type Typ;
    type Ref is access all Typ'Class;
    type Typ(LayoutManager2_I : Java.Awt.LayoutManager2.Ref;
             Serializable_I : Java.Io.Serializable.Ref)
     is new Java.Lang.Object.Typ
       with null record;
    ------------------------------
    -- Constructor Declarations --
    ------------------------------
    function New_BorderLayout (This : Ref := null)
                               return Ref;

    function New_BorderLayout (P1_Int : Java.Int;
                               P2_Int : Java.Int;
                               This : Ref := null)
                               return Ref;
    -------------------------
    -- Method Declarations --
    -------------------------
    procedure AddLayoutComponent (This : access Typ;
                                  P1_Component : access 
Standard.Java.Awt.Component.Typ'Class;
                                  P2_Object : access 
Standard.Java.Lang.Object.Typ'Class);
    function GetLayoutComponent (This : access Typ;
                                 P1_Object : access 
Standard.Java.Lang.Object.Typ'Class)
                                 return access Java.Awt.Component.Typ'Class;


Why choosing named access for New_BorderLayout and anonymous access for 
AddLayoutComponent or GetLayoutComponent for the type of parameters 
P1_xxx and the return type?
Why not all named or all anonymous ?

Thanks, Pascal.