On Fri, 10 Dec 2004 14:54:26 +0200, Peter Dimov <pdimov@mmltd.net> wrote:
Peder Holt wrote:
On Fri, 10 Dec 2004 03:50:58 -0700, Larry Evans <cppljevans@cox-internet.com> wrote:
On 12/10/2004 03:25 AM, Larry Evans wrote:
where the problem with typedef's is mentioned as the show-stopper.
Actually, Rani Sharoni's post in that thread is the best explanation I've seen to date.
Still, the problem in his post applies to typedefs. If A<T>::B is a nested class or struct under A<T>, and not a typedef, deduction should always be possible.
In the case where B is a typedef: typedef typename some_class<T> B; you can deduce some_class<T> instead of A<T>::B
No, you can't. Given some_class<V> as input to the pattern A<T>::B, you have no way to deduce T.
template<class T> struct A { typedef typename arbitrarily_complex_metafunction<T>::type B; };
And of course getting back to iterators, you have no way of determining whether T* is T*, vector<T, A>::iterator, or basic_string<T, Tr, A>::iterator, much less deducing A or Tr.
What I was trying to say, was that, given that there are no nested classes involved, arbitrarily_complex_metafunction<T>::type will in the end be reduced to arbitrary_complex_type<A0,A1,A2,...>, which is a concrete type which can be deduced. For the typeof library this is sufficient. On the other hand: template<class T> struct A { class B; }; A<T>::B now should give sufficient information to be deduced.
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