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From: Arkadiy Vertleyb (vertleyb_at_[hidden])
Date: 2004-12-02 00:21:02

"Allen Yao" <yaozhen_at_[hidden]> wrote

> (1) Is template template parameter supported?

They aren't.

> (2) In your opinion, is it just *possible* to support complex
> non-type template parameters suppose no matter how ugly the user interface
> will be?

It all depends on:

1) whether it is possible to represent this as a number of compile-time
integers, and
2) whether it's possible to return this as a result of a meta-function.

As far as my knowledge of the current state of template meta-programming
goes, I don't see how it's possible. OTOH, 3 months ago I thought integral
template parameters are impossible to support. And now, thanks to Peder, we
do have them :).

> In addition, I suggest adding a section in the document of the typeof
> library
> to mention the problems about complex non-type template parameters,
> dependendent
> non-type template parameters and template template parameters, including
> whether
> they are supported or not by the current library, and the possibility or
> main
> obstacles for supporting them in the future.

Good idea.

Actually there is one more limitation that keeps bothering me. It is
related to nested classes, and most unfortunate because of iterators. IOW,
we can't just register, e.g., std::vector<T>::const_iterator (as we do with
std::vector<T>), and the user always have to register concrete classes, like
std::vector<int>::const_iterator, std::vector<short>::const_iterator, etc.,
separately, as she needs them. This limitation comes from the "non-deduced
context", and applies at least to the compliant implementation, but I think
the vintage implementation should have the same problem :(



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