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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Constructors with multiple inheritance
Date: Thu, 10 Nov 2011 08:33:51 +0000
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Date: 2011-11-10T08:33:51+00:00
List-Id: <comp.lang.ada>

"Rego, P." <pvrego@gmail.com> writes:

> Maybe I can explain this easier trying to use C++. Let's suppose I
> have a class Par_Class with an integer and a pointer to a string. I
> could code, for example, (please correct me if I'm doing wrong)
>
> class Par_Class {
> public:
>   Par_Class (int aValue, const char *aName);
>
> private:
>   int theValue;
>   char *theName;
> };
>
> the constructor could be implemented as
>
> Par_Class::Par_Class (int aValue, const char *aName){
>   theValue = aValue;
>   strcpy (theName, aName);
> };
>
> and finally we could instantiate this class with
>
> Par_Class Par_Obj (23, "My object is this");
>
> and sure this constructor method belongs to the class Par_Class and
> not to any other class.

Par_Class (int aValue, const char *aName) is the very special C++
constructor syntax; when used the compiler generates a new blank area of
memory and the constructor gets to fill it in.

This is *not* the same as 

   function Construct 
     (P : access Par_Class; aValue : Integer; aName : Integer_Ptr)
      return Par_Class_Ptr;

which requires there to be a previous Par_Class instance; the nearest
(Ada 2012) equivalent is I think

   function Construct 
     (aValue : Integer; aName : Integer_Ptr)
      return Par_Class is
   begin
      return Result : Par_Class do
         Result.theValue := aValue;
         Result.theName := aName;
      end return;
   end Construct;

or, OK for Ada 95 and nearest to your present scheme:

   function Construct 
     (aValue : Integer; aName : Integer_Ptr)
      return Par_Class_Ptr is
      P_Ptr : constant Par_Class_Ptr := new Par_Class;
   begin
      P_Ptr.theValue := aValue;
      P_Ptr.theName := aName;
      return P_Ptr;
   end Construct;