questions to generic

questions to generic

[Rick Santa-Cruz]

Hi,

I have 2 questions:
1. ) Is it possible to create a generic procedure, which is not part of a 
package, something like:
procedure Gen_Test_Client is
 generic
  type Element is private;
 procedure Gen_Proc(Element: Element);
...
where Gen_Test_Client is the start-procedure?

2.) How is it possible to create a generic child package?


Thanks in advance,
Rick 

Re: questions to generic

[Georg Bauhaus]

Rick Santa-Cruz <rick_santa_cruz75@msn.com> wrote:
: Hi,
: 
: I have 2 questions:
: 1. ) Is it possible to create a generic procedure, which is not part of a 
: package,

yes, the way you have done.

: where Gen_Test_Client is the start-procedure?

no. It has to be instantiated somewhere to become a real procedure.

: 2.) How is it possible to create a generic child package?

You might find it useful to think of child packages as nested
packages. Consider the steps it takes to make an instance
of the outer package. After you have an instance of the outer
package, you are back at step 1, where you instantiate some generic
package :-)


-- Georg

Re: questions to generic

[Rick Santa-Cruz]

Hi,

> yes, the way you have done.
>
> : where Gen_Test_Client is the start-procedure?
>
> no. It has to be instantiated somewhere to become a real procedure.
And how and where do I have to instantiate the procedure then?

>
> : 2.) How is it possible to create a generic child package?
>
> You might find it useful to think of child packages as nested
> packages. Consider the steps it takes to make an instance
> of the outer package. After you have an instance of the outer
> package, you are back at step 1, where you instantiate some generic
> package :-)
So is it this way correct:
package Pack1 is
 generic
  type Element is private;
 package Child_Pack is
  procedure Proc(El: Element);
 end Child_Pack;
end Pack1;

--body
package body Pack1 is
 package bodY Child_Pack is
  procedure Proc(El: Element) is
   El1: Element;
  begin
   El1:= El;
  end Proc;
 end Child_Pack;
end Pack1;

-- test-client:
with Pack1; -- by the way when I write here: with Pack1.Child_Pack; I get a 
compilation-error. Why?
procedure Gen_Test_Client is
  package S_2 is new Pack1.Child_Pack(Integer);
....


Thanks,
Rick 

Re: questions to generic

[Georg Bauhaus]

Rick Santa-Cruz <rick_santa_cruz75@msn.com> wrote:
: Hi,
: 
:> yes, the way you have done.
:>
:> : where Gen_Test_Client is the start-procedure?
:>
:> no. It has to be instantiated somewhere to become a real procedure.
: And how and where do I have to instantiate the procedure then?

wherever you like :)

: So is it this way correct:

Does you compiler report anything?

: -- test-client:
: with Pack1; -- by the way when I write here: with Pack1.Child_Pack; I get a 
: compilation-error. Why?

That's the point. Pack1 is generic, it is not an instance.
By writing Some_Package.Something_Else, you are referring
to Something_Else in a real package (which can be a plain
package, or an real instance of a generic package).
Imagine you had a generic package as before,
with a nested generic. But the formal parameter of the
nested generic is different from the formal parameter of
the outer package.
The outer is instantiated with some actual type. What have
you got?


-- Georg

Re: questions to generic

[Björn Persson]

Georg Bauhaus wrote:

> That's the point. Pack1 is generic, it is not an instance.

No, Child_Pack is generic. Pack1 isn't.

-- 
Björn Persson                              PGP key A88682FD
                    omb jor ers @sv ge.
                    r o.b n.p son eri nu

Re: questions to generic

[Georg Bauhaus]

Bj�rn Persson <spam-away@nowhere.nil> wrote:
: Georg Bauhaus wrote:
: 
:> That's the point. Pack1 is generic, it is not an instance.
: 
: No, Child_Pack is generic. Pack1 isn't.

Right. I was stuck in my own explaination of outer generic
and inner generic.


-- Georg

Re: questions to generic

[Björn Persson]

Rick Santa-Cruz wrote:

> And how and where do I have to instantiate the procedure then?

For example:

procedure Gen_Test_Client is

    generic
       type Element is private;
    procedure Gen_Proc(El: Element);

    procedure Gen_Proc(El: Element) is
    begin
       null;
    end Gen_Proc;

    procedure Natural_Proc is new Gen_Proc(Natural);
    procedure Character_Proc is new Gen_Proc(Character);

begin  --  Gen_Test_Client
    Natural_Proc(5);
    Character_Proc('X');
end Gen_Test_Client;

> So is it this way correct:
> package Pack1 is
>  generic
>   type Element is private;
>  package Child_Pack is
>   procedure Proc(El: Element);
>  end Child_Pack;
> end Pack1;

Strictly speaking, that's a subpackage. A child package is specified 
separately. (With Gnat it will be in its own file.)

package Parent is
    package Subpackage is
    end Subpackage;
end Parent;

package Parent.Child_Package is
end Parent.Child_Package;

> with Pack1; -- by the way when I write here: with Pack1.Child_Pack; I get a 
> compilation-error. Why?

When you write "with Pack1;" you get access to everything in Pack1, 
including subpackages. For a child package you'd have to write "with 
Parent.Child_Package;".

-- 
Björn Persson                              PGP key A88682FD
                    omb jor ers @sv ge.
                    r o.b n.p son eri nu