Re: Incomplete types used with generics

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

"Jeremiah" <jeremiah.breeden@gmail.com> wrote in message 
news:830c0323-a06c-4884-9214-89f3ee6f17b5@googlegroups.com...
...
> I *think* the generic parameter "type Item_Type is tagged limited 
> private;" is considered incomplete as is "type Node2_Type is tagged;".

On the the things that *I* missed is the above. No, private types aren't 
incomplete, and in fact even a private type cannot be used as the actual to 
a generic private type (the type is immediately frozen, but for a private 
type that is illegal, as per 13.14(17)).

If you want an incomplete formal parameter, you have to write it that way. 
That is:

    type Item_Type is tagged;

On the other side, *anything* can be the actual to a generic formal 
incomplete type. The type can be limited, incomplete, private, and/or 
abstract. Of course, that means there isn't much you can do with such a type 
(you'd have to pass in an allocator and deallocator subprogram, for 
instance). There's somewhat more you can do with a tagged incomplete type 
(in particular, you can make calls), but even that is very limiting. But of 
course that's the idea; if you can live with the limitations, you get the 
ability to instantiation the generic almost anywhere with any kind of type.

>> What am I missing?

That you didn't use an incomplete formal type, so OF COURSE the compiler 
rejected your instantiation with an incomplete type. Sorry about missing 
that yesterday; I was so excited that someone would actually try to use an 
incomplete formal that I failed to notice that you didn't actually do so. 
One does not think clearly when you are gloating. :-)

                                        Randy.