Re: Ada Queue

[Simon Wright <simon@pogner.demon.co.uk>]

"Joseph T." <thisthat7@hotmail.com> writes:

> Can anyone corroborate why I chose to make this enqueue function using the
> passed pointer to Q instead of the temp pointer to loop through the queue?
>  Any suggestions, ideas, compliments, critiques are greatly appreciated.
>  Please help.
> 
> procedure Enqueue(Q: in out Queue; E : Element_type) is
>    New_Queue : Queue;
> 
> begin
>    if Q /= null then
>        New_Queue := Q;
>        while Q.Rest /= null loop
>           Q := Q.Rest;
>        end loop;
>        Q.Rest := new QueueNode;
>        Q := Q.Rest;
>        Q.Data := E;
>        Q.Rest := null;
>        Q := New_Queue;
>    else
>        Q := new QueueNode;
>        Q.Data := E;
>        Q.Rest := null;
>    end if;
> end Enqueue;

Personally I don't think you should mess with the parameter like
this. The temporary variable is the one you should use for traversing
the Queue to find its end.

   procedure Enqueue(Q: in out Queue; E : Element_type) is
   begin
     if Q /= null then
       declare
	 Last : Queue := Q;
       begin
	 while Last.Rest /= null loop
	   Last := Last.Rest;
	 end loop;
	 Last.Rest := new QueueNode'(Data => E,
				     Rest => null);
       end;
     else
       Q := new QueueNode'(Data => E,
			   Rest => null);
     end if;
   end Enqueue;