Errors when typdef'ing hash_map::iterator

[Matt Fischer]

On 4/18/07, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> On 16/04/07, Matt Fischer <mattfischer84@gmail.com> wrote:
> > Hi all.  I've run into a problem using the hash_map extension class in
> > libstdc++, and I'm evidently not well-versed enough in templates to
> > determine what the root cause is.  Essentially the problem I'm seeing
> > arises when I attempt to make a typedef of a hash_map iterator which
> > references a forward-declared class.
>
> That's not allowed when Foo is not complete, and neither is the
> map<int, Foo>  (but it doesn't fail unless you turn on concept-checks
> with -D_GLIBCXX_CONCEPT_CHECKS)
>
> Unless explicitly stated otherwise (as with e.g. std::tr1::shared_ptr)
> all types used as template arguments to templates in the standard
> library must be complete.  Although hash_map isn't in the standard it
> seems to have the same requirement, and so fails with the error you're
> seeing.
>
> Jon
>
Ah, I was wondering if this might not be the case.  So the fact that
std::map works with incomplete types is really an example of undefined
behavior, and presumably the code I'm porting is written that way
because in VC++'s library implementation that just so happens to be
true for hash_map as well.  Thank you for your help.

--Matt