Re: Intervention needed?

["Randy Brukardt" <randy@rrsoftware.com>]

"Jere" <jhb.chat@gmail.com> wrote in message 
news:94a74b21-9c35-4f90-90f8-6262cde49e20@googlegroups.com...
...
> You would think that a container of limited types would be very 
> restrictive,
> but with the advent of Implicit_Dereference and reference types, there
> is definitely some meat there.  I would say maps and lists are the two
> areas I find the most need.

A container of a limited type would be very restrictive. ;-)

Several of us (including me) have tried to imagine how a container of 
limited objects would work, but it just doesn't make much sense. The primary 
problem is that one cannot control the lifetime of objects in a container, 
which includes the problem that one can't control the initialization of 
objects in a container. Whereas for non-limited objects, one just replaces 
them with the right data, you can't do that for a limited object. And since 
the initialization needs are type-dependent, there's no good way to deal 
with it in a type-safe manner. (A constructor with an unknown set of 
parameters isn't going to be type-safe, and with any particular set of 
parameters is too limiting.

Note that the same sort of thing applies to controlled objects -- it's not 
recommended to put controlled objects into any of the Ada.Containers with 
the possible exception of the undefinite containers. That's because the 
creation and destruction of objects is up to the container, not under any 
sort of program control. (Deleting an element does not necessarily delete 
the object.)

                             Randy.