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From: "Rick Santa-Cruz" <rick_santa_cruz75@msn.com>
Newsgroups: comp.lang.ada
Subject: Re: implicit cast and inheritance
Date: Sat, 2 Oct 2004 18:32:04 +0200
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Date: 2004-10-02T18:32:04+02:00
List-Id: <comp.lang.ada>

Hi,

>> I have a small question. See the following source-code:
>> package Pack is
>>     type Base is tagged
>>         record
>>             Value: Integer;
>>         end record;
>>     procedure Base_Proc(B: Base);
>>
>>     type Derived is new Base with
>>         null record;
>> end Pack;
>>
>> And now I have the following source for the main-procedure:
>> with Pack;
>> use Pack;
>>
>> procedure main is
>>     B: Base;
>>     D: Derived;
>>     procedure Proc(B: Base) is
>>     begin
>>         null;
>>     end Proc;
>> begin
>>     Pack.Base_Proc(B);    -- 1
>>     Pack.Base_Proc(D);    -- 2
>>     Proc(B);   -- 3
>>     Proc(D);    -- 4
>> end main;
>>
>
> In this case, there is one compiled version of the body of Base_Proc,
> and the call Base_Proc (D) calls it. D is passed by reference, so the
> body doesn't know or care whether it is getting a Base type or a
> Derived type.
So an implict cast will be done from Derived to Base, so that the body of 
the Base_Proc(B: Base) method can be called. Is this correct?
You told me, that in the package the following will be declared:
procedure Base_Proc (B : Derived);
But what's then with the body of Pack? Will there be an body of Base_Proc(B: 
Derived) which is the same as Base_Proc(B: Base),  or how does it work?

>> If it is in the same package, is then always implicitly done a cast,
>> or is the procedure Base_Proc in the derived class "Derived"
>> automatically defined with a parameter Type "Derived"?
>
> There is a difference between declaring a subprogram and providing an
> implementation for it.
Sadly, I don't understand what you mean with this.

Thanks in advance,
Rick