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From: Martin Dowie <martin@re.mo.ve.thedowies.com>
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Subject: Re: Pop function
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Date: Wed, 14 Dec 2011 18:29:09 -0600
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Date: 2011-12-14T18:29:09-06:00
List-Id: <comp.lang.ada>

"Rego, P." <pvrego@gmail.com> wrote:
> Hello, 
> 
> Given a list type 
>    type T_List is
>       record
>          Next : access T_List;
>          Item : Integer;
>       end record;
>    T_List_Ptr is access T_List;
> 
> Is it right to implement a pop function like the following? (Free is an
> Unchecked_Deallocation)
>    function Pop (Sender : access T_List) return Integer is
>       Current_Sender_Ptr : T_List_Ptr := T_List_Ptr (Sender);
>       Current_Item : constant T_List := Sender.Item;
>    begin
>       if Sender /= null then
>          if Sender.Next /= null then
>             Current_Sender_Ptr := T_List_Ptr (Current_Sender_Ptr.Next);
>          end if;
> 		 Free (Current_Sender_Ptr);
>          return Current_Item;
>       else 
>          return 0;
>       end if;
>    end Pop;
> 
> I mean, if I set Current_Sender_Ptr := T_List_Ptr
> (Current_Sender_Ptr.Next), it's equivalent to Sender := Sender.Next?
> (which I could not do directly due to in this case it would not be
> allowed an anonymous reference, right?)

If Sender is null, your in trouble before you get to "begin".

Also, is it really ok to return 0 from an empty list rather than raising an
exception?

What does Sender "point to" on return if the head of the list is removed?

-- Martin
-- 
-- Sent from my iPad