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From: markus034@gmail.com
Newsgroups: comp.lang.ada
Subject: Re: Translating C++ class types into Ada tagged types?
Date: Sun, 15 Jul 2007 22:47:13 -0700
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Date: 2007-07-15T22:47:13-07:00
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On Jul 10, 1:07 am, Georg Bauhaus <bauhaus.rm.t...@maps.futureapps.de>
wrote:
> jimmaureenrog...@worldnet.att.net wrote:
>
> > Ada is object oriented, but does not provide constructors or
> > destructors. The following code is similar to your example
> > without constructors or destructors.
>
> Just to add that Ada does have construction and destruction
> (I am sure Jim Rogers knows them well), the language provides
> a number of ways to make sure that initialization and
> finalization takes place (and when it takes place!).
> So "Cat Frisky(5)" can be expressed in Ada as well, just not
> using constructors as in C++.
>
> One such facility well suited to polymorphic objects uses a
> factory function such as
>
>    function Make
>      (species: String; age: Natural) return Animal'class;
>     -- an animal as requested in `species`, `age` years old
>
> where Animal could be a superclass of Cat in C++ terms.
> The 'class in Animal'class means that Make will return an object
> from the Animal hierarchy. If you wanted just a Cat or more
> specific heirs of Cat, say a cat that has fur of some color,
> use
>
>    function Make
>      (fur_color: Color; age: Natural) return Cat'class;
>     -- some cat whose fur has the given `fur_color`,
>     -- `age` years old
>
> And, finally, a simple construction function for Cat specifically
> and not heirs, but simply Cats could be
>
>    function Make
>      (age: Natural) return Cat;
>     -- a cat, `age` years old
>
> (Unlike C++, Ada can use the type of the return value (Cat)
> in order to decide what specific type of object to expect on
> the LHS of ":=", for example.)
>
> This isn't the only way to initialize objects, either
> at run-time, or at compile time. In particular, you can
> have default initialization etc..
>
>  -- Georg

In two programs written bellow i would like to ask you the following
questions:
-In "program 1" i used the constructor function. However, I don't
understand how
to make methods, like Object.method, with the constructor function.
Does anyone know
how to make  methods with the constructor function in program 1?
-In "program 2" i didn't use any constructor function. My question is
do i need to make
any constructor function in program 2?

Program 1 (with consructors but without methods):

--spec 1.
PACKAGE Persons IS

   TYPE Genders IS (Female, Male);

   SUBTYPE NameRange IS Positive RANGE 1..20;
   SUBTYPE NameType IS String(NameRange);

   TYPE Person IS TAGGED PRIVATE;

   --Selectors
   FUNCTION NameOf(Whom:Person) RETURN NameType;
   FUNCTION GenderOf(Whom:Person) RETURN Genders;

   PROCEDURE Put(Item:IN Person);

   PACKAGE Constructors IS
      --constructor function

      FUNCTION MakePerson(Name:String;
                          Gender:Genders) RETURN Person;

   END Constructors;

   PRIVATE
   TYPE Person IS TAGGED RECORD
      NameLength:NameRange:=1;
      NameField:NameType:=(OTHERS =>' ');
      Gender:Genders:=Female;
   END RECORD;


END Persons;
--spec 2.
WITH Persons; USE Persons;

PACKAGE Employees IS


   TYPE Employee IS NEW Person WITH PRIVATE;

   TYPE IDType IS NEW Positive RANGE 1111..9999;

   --Selectors
   FUNCTION IDOf(Whom:Employee) RETURN IDType;

   PROCEDURE Put(Item:IN Employee);

   PACKAGE Constructors IS
      --constructor function

      FUNCTION MakeEmployee(Name:String;
                            Gender:Genders;
                            ID:IDType) RETURN Employee;


   END Constructors;

   PRIVATE
   TYPE Employee IS NEW Person WITH RECORD
      ID:IDType:=1111;
   END RECORD;


END Employees;

--body 1.
WITH Ada.Text_IO;
USE Ada.Text_IO;

PACKAGE BODY Persons IS

   PACKAGE Gender_IO IS NEW Enumeration_IO(Enum=>Genders);

--   TYPE Genders IS (Female, Male);

--   SUBTYPE NameRange IS Positive RANGE 1..20;
--   SUBTYPE NameType IS String(NameRange);

--   TYPE Person IS TAGGED PRIVATE;

   --Selectors
   FUNCTION NameOf(Whom:Person) RETURN NameType IS
   BEGIN
      RETURN Whom.NameField;
   END NameOf;

   FUNCTION GenderOf(Whom:Person) RETURN Genders IS
   BEGIN
      RETURN Whom.Gender;
   END GenderOf;


   PROCEDURE Put(Item:IN Person) IS
   BEGIN
      Put(Item => "Name: ");
      Put(Item => Item.NameField(1..Item.NameLength));
      New_Line;

      Put(Item => "Gender: ");
      Gender_Io.Put(Item=>Item.Gender, Set=>Lower_Case);
      New_Line;

   END Put;


   PACKAGE BODY Constructors IS
      --constructor function
      FUNCTION MakePerson(Name:String;
                          Gender:Genders) RETURN Person IS
      Temp:NameType;
      BEGIN
         Temp(1..Name'Length):=Name;

         RETURN (NameLength=>Name'Length,
                 NameField=>Temp,
                 Gender=>Gender);

      END MakePerson;


   END Constructors;

--   PRIVATE
--   TYPE Person IS TAGGED RECORD
--      NameLength:NameRange:=1;
--      NameField:NameType:=(OTHERS =>' ');
--      Gender:Genders:=Female;
--   END RECORD;
--

END Persons;
--body 2.
WITH Ada.Text_IO; USE Ada.Text_IO;
WITH Ada.Integer_Text_IO; USE Ada.Integer_Text_IO;

PACKAGE BODY Employees IS


   PACKAGE BODY Constructors IS
      --constructor function
      FUNCTION MakeEmployee(Name:String;
                            Gender:Genders;
                            ID:IDType) RETURN Employee is
      BEGIN
         RETURN (Persons.Constructors.MakePerson(
            Name=>Name,
            Gender=>Gender)
            WITH
            ID=>ID);

      END MakeEmployee;


   END Constructors;

      --Selectors
   FUNCTION IDOf(Whom:Employee) RETURN IDType IS
   BEGIN
      RETURN Whom.ID;
   END IDOf;

   PROCEDURE Put(Item:IN Employee) IS
   BEGIN
      Persons.Put(Item => Persons.Person(Item));

      Put(Item => "ID Number: ");
      Put(Item => Positive(Item.ID), Width=>1);

   END Put;

END Employees;


--main program
WITH Ada.Text_IO; USE Ada.Text_IO;
WITH Persons; USE Persons;
WITH Employees; USE Employees;

PROCEDURE Main IS
   George:Person;
   Mary:Employee;
BEGIN
   --first construct a person and an employee
   George:=Persons.Constructors.MakePerson(
      Name=>"George",
      Gender=> Male);

   Mary:=Employees.Constructors.MakeEmployee(
      Name=>"Mary",
      Gender=>Female,
      ID=>1234);


   --Now display them
   Put(Item => George);
   Put_Line(Item => "--------------------");
   Put(Item => Mary);

END Main;


Program 2 (without constructors but with methods):

--spec 1
package People is
   type Person is tagged private;
   function Get_Age(The_Person : Person) return Positive;
   procedure Set_Age(The_Person : in out Person; Age : in Positive);
   procedure Sing(The_Person : Person);
private
   type Person is tagged record
      Age : Positive;
   end record;
end People;

--body 1

WITH Ada.Text_IO;

package body People is

   -------------
   -- Get_Age --
   -------------

   function Get_Age (The_Person : Person) return Positive is
   begin
      return The_Person.Age;
   end Get_Age;

   -------------
   -- Set_Age --
   -------------

   procedure Set_Age (The_Person : in out Person; Age : in Positive)
is
   begin
      The_Person.Age := Age;
   end Set_Age;

   ----------
   -- Sing --
   ----------

   procedure Sing(The_Person : Person) is
   begin
      Ada.Text_IO.Put_Line("         Can sing.");
   end Sing;

end People;

--spec2
WITH People; USE People;

PACKAGE Programmers IS

   TYPE Programmer IS TAGGED PRIVATE;

   function Get_Age(The_Programmer : Programmer) return Positive;
   procedure Set_Age(The_Programmer : in out Programmer; Age : in
Positive);
   procedure Program(The_Programmer : Programmer);
private
   type Programmer is new Person with record
      Age : Positive;
   end record;
end Programmers;

--body 2

WITH Ada.Text_IO;

package body Programmers is

   -------------
   -- Get_Age --
   -------------

   function Get_Age (The_Programmer : Programmer) return Positive is
   begin
      return The_Programmer.Age;
   end Get_Age;

   -------------
   -- Set_Age --
   -------------

   procedure Set_Age (The_Programmer : in out Programmer; Age : in
Positive) is
   begin
      The_Programmer.Age := Age;
   end Set_Age;

   -------------
   -- Program --
   -------------

   procedure Program(The_Programmer : Programmer) is
   begin
      Ada.Text_IO.Put_Line("       Can program.");
   end Program;

end Programmers;


--main program
WITH People;
WITH Programmers;
USE TYPE People.Person;
USE TYPE Programmers.Programmer;
WITH Ada.Text_Io;

procedure Person_Main is
   George : People.Person;
   Andy:Programmers.Programmer;
begin
   George.Set_Age(20);
   Andy.Set_Age(29);

   Ada.Text_Io.Put("George: ");
   Ada.Text_Io.Put_Line(Positive'Image(George.Get_Age) & " years
old.");
   Ada.Text_IO.New_Line;
   George.Sing;
   Ada.Text_IO.Put_Line(Item => "--------------------");
   Ada.Text_Io.Put("Andy: ");
   Ada.Text_Io.Put_Line(Positive'Image(Andy.Get_Age) & " years old.");
   Ada.Text_IO.New_Line;
   Andy.Program;
end Person_Main;