[boost] [scope_exit] C++11 freely uses typename (on MSVC10?)

Subject: [boost] [scope_exit] C++11 freely uses typename (on MSVC10?)
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2012-04-03 09:59:50

Nathan Ridge wrote
> 
>>>> For example, is the following supposed to compile on MSVC10?
>>>> #include <boost/mpl/identity.hpp>
>>>> 
>>>> int main() {
>>>>     typedef typename boost::mpl::identity<int>::type t;
>>>>     t i = 0;
>>>>     return i;
>>>> }
>>> 
>>> This code does not compile on my copy of MSVC10.
>>> 
>>> -->error C2899: typename cannot be used outside a template declaration
>>> 
>> 
>> Thanks. Is anyone positive about what the C++11 standard says in this
>> case?
>> This code compiles on my GCC 4.5.3 with -std=c++0x... who's right MSVC or
>> GCC?
> 
> C++03 section 14.2 paragraph 5 says:
> 
> "[Note: just as is the case with the typename prefix, the template prefix
> is 
> allowed in cases where it is not strictly necessary; i.e., when the
> expression 
> on the left of the -> or ., or the nested-name-specifier is not dependent
> on a 
> template-parameter.]"
> 
> C++11 amends this to:
> 
> "[Note: As is the case with the typename prefix, the template prefix is
> allowed 
> in cases where it is not strictly necessary; i.e., when the
> nested-name-specifier 
> or the expression on the left of the -> or . is not dependent on a 
> template-parameter, or the use does not appear in the scope of a
> template.]"
> 
> The addition of "or the use does not appear in the scope of a template"
> makes
> your example valid in C++11 (but it was invalid in C++03).
> 
> It seems recent versions of GCC have adopted the C++11 behaviour, but MSVC
> has 
> not (yet, as of version 10).
> 

I see. Thanks.
--Lorenzo

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