Re: Problem with generic linked list package

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 08/10/2014 02:57 PM, Simon Wright wrote:
>
> You have (after Shark8's suggestion, I think) a generic package which
> starts something like
>
>     generic
>        type T is private;
>        with function "<" (L, R : T) return Boolean is <>;
>     package P is

Specifically, a linked-list pkg, which only uses "<" for its Insert_In_Order 
subprogram. There are plenty of times when you want to keep things in a list and 
don't care about their order; this pkg requires that the client supply a "<" 
that will never be used in that case. And there are times when you want to 
allocate things like tasks and keep them in a data structure such as a linked 
list. There is no meaningful definition of "<" in such a case.

task type T;

type T_Ptr is access T;

How would one create a linked list of T_Ptr? One could fake up a "<" that 
returns True, but that's wasted effort.

The intention of my post which started off this sub-thread (about writing "<" 
for record types) was to get the OP thinking about how to write a linked-list 
pkg that would be useful for such a case (not requiring "<" to be instantiated) 
but still able to provide Insert_In_Order for cases where "<" is meaningful and 
an ordered list is desired.

-- 
Jeff Carter
"Little blondes with long hair and short skirts and
boots and big chests and bright, witty, and perceptive."
Play It Again, Sam
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