Re: Some questions

["David C. Hoos" <david.c.hoos.sr@ada95.com>]

----- Original Message ----- 
From: "Sim Con" <sicon@hotmail.com>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada.eu.org>
Sent: Thursday, October 10, 2002 6:17 AM
Subject: Some questions


<snip>
> the compilator says "child of an instance must be an instance or
> renaming", so what's wrong? How can i build custom procedures for print
> the generic elements in generic packages???
What you need to do is provide a print procedure when you instantiate the
generic.
This is done by declaring the generic like this:

generic
    type Item is private;
    with Procedure Print (I : Item) is <>;
package stacks
   type Stack is private;
.
   procedure Print (S : Stack);
.
end Stacks;

Then, when you instantiate the package, you do it specifying the type
if the items in the stack, and a print procedure for that type -- e.g.,:

package stack_float is new Stacks (float, print_float);

where print_float is your print procedure for the float type.

The <> in the generic declaration means that if there is a procedure
named Print visible at the point of instantiation, and having a parameter
profile matching that of the formal procedure parameter of your generic
declaration, then the instantiation can simply be
package stack_float is new Stacks (float);
because the matching print procedure will be included by default.

Then within your implementation of the generic package's Print procedure,
you can call the Print (I : Item) procedure for each item in the stack.