oo programing question

oo programing question

[shoko]

i have the following code:

package a is
  --car class --
  type a is tagged private; 
  type a_ptr is access all car'class;
  
  --car methods --
   private
     type a is tagged 
     record
         name:String(1..256);
     end record;
  
   
end a;
-------------------------------------

with a;

package b is
   type b is new a.a with private;   <--  constraint error 
   type b_Ptr is access all b'Class;

   function init_b(maximum:positive) return b_Ptr;
  
  private
     type b is new  a.awith
     record
         maximum_:positive;
     end record;
end b;
-------------------------------------------
in the main procedure:

with a;use a;
with b;use b;

procedure main is
   new_b:b_ptr;
     
begin
    new_b := init_b(90);
 end main;

i get constraint error on b.ads
i dont understand why

please help

Re: oo programing question

[Stephen Leake]

shoko2004@hotmail.com (shoko) writes:

> i have the following code:

After fixing the obvious typos, I get no constraint error. In any
case, you can't get a constraint error just running the compiler;
that's a runtime error. Since you don't provide a body for package b,
I can't run 'main'.

Please post complete, compilable examples. Be sure you run the
compiler on the actual code you post; don't make edits after copying
to your news client. If you are getting a runtime error, show the
execution command line, and the error message you get.

-- 
-- Stephe

Re: oo programing question

[Martin Krischik]

shoko wrote:

> i have the following code:
> 
> package a is
>   --car class --
>   type a is tagged private;

There are two schools here:

1. Packages are multiples and objects are singles:

package Cars is
type Car is ...

2. Packages are singles and objects are Object:

Package Car is
type Object is

Calling the Type the same as the package gets you into trouble when code
becomes more complex.

>   type a_ptr is access all car'class;

Use "access" and not "access all" whenever possible.
   
> with a;
> 
> package b is
>    type b is new a.a with private;   <--  constraint error
>    type b_Ptr is access all b'Class;
> 
>    function init_b(maximum:positive) return b_Ptr;

Are you shure you need a access here? Adas stack handling is far more
powerfull then C++'s. So you might be better of just to return 'b'. Look at
New_Object in

http://adacl.sourceforge.net/html
______Include__AdaCL-SAR-Filter-Replace__adb.htm


>   private
>      type b is new  a.awith
>      record
>          maximum_:positive;
>      end record;
> end b;
> -------------------------------------------
> in the main procedure:
> 
> with a;use a;
> with b;use b;

don't "use" everything. 
 
> procedure main is
>    new_b:b_ptr;
>      
> begin
>     new_b := init_b(90);
>  end main;
> 
> i get constraint error on b.ads
> i dont understand why

Difficult without the package bodys.

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://adacl.sourceforge.net

oo programing question

[shoko]

here is my generic package:
generic
   type Element_Type is private;

   package queue is
     type Queue  is abstract tagged private; 
     
     type newqueue is new Queue ;<-- how to create new queue type?
     
     procedure Init( Q: in out Queue) is abstract;

     private
         type Queue is  abstract tagged 
           record
              value:Element_Type;
           end record;
   
   end queue; 

i need to create a new abstract type(newqueue) that will inherit from Queue.

  
then need to put the new type(newqueue) in the same generic Queue package,
and to add a new method to the new abstract type.

the reason that the new abstract type(newqueue) should be in the same package is:
i have a type that inherit from Queue  
and now i need a new type that inherit from the new abstract type (newqueue)
and will be the same as the one that inherit from Queue.

how can i do it?

thanks

Re: oo programing question

[Martin Krischik]

shoko wrote:

> here is my generic package:
> generic
>    type Element_Type is private;
> 
>    package queue is
>      type Queue  is abstract tagged private;
>      
>      type newqueue is new Queue ;<-- how to create new queue type?

   type New_Queue is tagged new Queue with private ;
      
>      procedure Init( Q: in out Queue) is abstract;

Just a thought:

function New_Queue return Queue;
 
>      private
>          type Queue is  abstract tagged
>            record
>               value:Element_Type;
>            end record;
>    
>    end queue;
> 
> i need to create a new abstract type(newqueue) that will inherit from
> Queue.
> 
>   
> then need to put the new type(newqueue) in the same generic Queue package,
> and to add a new method to the new abstract type.
> 
> the reason that the new abstract type(newqueue) should be in the same
> package is: i have a type that inherit from Queue
> and now i need a new type that inherit from the new abstract type
> (newqueue) and will be the same as the one that inherit from Queue.

This might still be possible with a child package.

With Regards

Martin


-- 
mailto://krischik@users.sourceforge.net
http://adacl.sourceforge.net