From: David Abrahams (dave_at_[hidden])
Date: 2008-03-28 15:53:51
on Fri Mar 28 2008, Steven Watanabe <watanabesj-AT-gmail.com> wrote:
> David Abrahams wrote:
>> on Fri Mar 28 2008, Steven Watanabe <watanabesj-AT-gmail.com> wrote:
>>> It can break today under certain conditions.
>> I don't understand how that is a case of what I'm describing. It looks
>> like a simple instantiation failure.
> Yep. The problem turns out to be that ADL causes msvc to instantate
> all the template parameters recursively.
> The result is that any constructs
> involving templates that cannot be instantiated cannot safely appear
> in the interfaces of non-metafunction class templates.
Actually I think they can if you wrap them appropriately:
I don't think function types have associated namespaces, do they?
> This means that using MPL lambda expressions as a replacement for
> template template parameters for instance doesn't work in general.
Bleah, that's ugly.
>> In C++0x you won't even be able to
>> typedef vector<foo(bar)> x;
>> without getting an error.
> And this is better than the possibility of obscure errors when
> the compiler unexpectedly instantiates vector<foo(bar)>
It's "better" as long as you're not trying to do the kinds of things we
do with MPL lambdas and related constructs like many of those that
appear in Proto.
-- Dave Abrahams Boost Consulting http://boost-consulting.com
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