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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: grassroots thoughts on access types
Date: Thu, 8 Feb 2018 19:23:47 -0600
Organization: JSA Research & Innovation
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Xref: reader02.eternal-september.org comp.lang.ada:50333
Date: 2018-02-08T19:23:47-06:00
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"Mehdi Saada" <00120260a@gmail.com> wrote in message 
news:5d9134c9-a7d4-468e-8685-ebbb393eabea@googlegroups.com...
> In my corrected exercices, I can read:
>
> package P_Token.F is
>   type T_Ptr_Token is access all T_Token'Class;
> end P_Token.F;
>
> package body  P_Token.Operateur.F is
>
>   type T_Ptr_Token_Operateur is access all T_Token_Operateur;
>
>   function Set_Ptr (Elem : in T_Operateur) return T_Ptr_Token is
>      Ptr_Token : T_Ptr_Token_Operateur;
>   begin
>      Ptr_Token := new T_Token_Operateur;
>      Initialisation(Ptr_Token.all,Elem);
>      return Ptr_Token.all'access; -- @@@ HERE

You could also have written:
      return T_Ptr_Token(Ptr_Token);

Generally, type conversions for general access types are equivalent to 
".all'Access".

>   end Set_Ptr;
>
> end P_Token.Operateur.F;
>
> and
>
> I understand the line marked (took me several minutes though ;-) ) but not 
> the logic. Instead of
> function Set_Ptr (Elem : in T_Operateur) return T_Ptr_Token is
>      Ptr_Token : T_Ptr_Token_Operateur;
> can we write:
> function Set_Ptr (Elem : in T_Operateur) return T_Ptr_Token is
>      Ptr_Token : T_Ptr_Token;
> ? What's the difference regards to implementation, memory usage or 
> anything ?
> T_TOKEN is a null tagged record type, T_TOKEN_OPERATEUR has one more 
> enumerative component.

No difference that I can see. T_Ptr_Token_Operateur seems like a totally 
unnecessary type to me, since the allocator would work just as well with 
T_Ptr_Token. (But I haven't tried this in an actual compiler, so I might 
have forgotten something subtle.)

                                       Randy.