Re: generic with procedure

From: Stephen Leake (stephen_leake_at_acm.org)
Date: 09/29/04 

Date: 28 Sep 2004 19:56:25 -0400
To: comp.lang.ada@ada-france.org

"Rick Santa-Cruz" <rick_santa_cruz75@msn.com> writes:

> Hi,
>
> I am starting to read a bit about generic programming and I am a bit
> confused from it, cause it seems to me a bit different to
> template-programming in C++.
> Sadly I can't figure out the difference between the following:
> 1.) generic
> type Element is private;
> package MyContainers is
> type MyContainer is private;
> procedure Some_Proc(Item : Element);
> end MyContainer;

This is a complete package spec.

> 2.) generic
> type Element is private;
> package MyContainers is
> type MyContainer is private;
> generic
> with procedure Some_Proc(Item : Element);
> end MyContainer;

This is not legal syntax. You could mean:

2a.)
generic
   type Element is private;
package MyContainer_2a is
   type MyContainer is private;
   
   generic
      with procedure Some_Proc(Item : Element);
   procedure Foo;
end MyContainer_2a;

or

2b.)
generic
   type Element is private;
package MyContainer_2b is
   type MyContainer is private;
   
   generic
   procedure Some_Proc(Item : Element);
   
end MyContainer_2b;

In 2a, 'Foo' is a generic procedure, that requires a generic formal
procedure parameter; presumably Foo calls Some_Proc in its body.

In 2b, 'Some_Proc' is a generic procedure, with no generic formal
parameters.

Here are some legal instantiations:

package Container_2a is new My_Container_2a (Integer);

procedure Proc (Item : Element) is
    Put_Line ("hello 2a");
end Proc;

procedure Bar is new Container_2a.Foo (Proc);

package Container_2b is new My_Container_2b (Integer);

procedure Proc is new Container_2b.Some_Proc; 

-- 
-- Stephe