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

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

lcaminiti
Hi all,

Isn't it C++11 supposed to allow to use typename freely even outside type-dependent context? Does MSVC10 support this?

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;
}

Note: Using typename freely will allow me to not introduce SCOPE_EXIT_ALL_TPL and still support this_ (not just this).

Thanks.
--Lorenzo
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Re: [scope_exit] C++11 freely uses typename (on MSVC10?)

Nelson, Erik - 2
Lcaminiti wrote on Monday, April 02, 2012 1:53 PM
 
> 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

Erik

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

lcaminiti
Nelson, Erik - 2 wrote
Lcaminiti wrote on Monday, April 02, 2012 1:53 PM
 
> 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?

Thanks a lot.
--Lorenzo
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Re: [scope_exit] C++11 freely uses typename (on MSVC10?)

Vicente Botet
Le 02/04/12 22:04, lcaminiti a écrit :

> Nelson, Erik - 2 wrote
>> Lcaminiti wrote on Monday, April 02, 2012 1:53 PM
>>
>>> For example, is the following supposed to compile on MSVC10?
>>> #include&lt;boost/mpl/identity.hpp&gt;
>>>
>>> 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?
>
>
I don't know what the c++11 standard says, but as there are some
compilers that don't support it and this was not allowed on C++03
compilers you should live with this constraint and the use of typename
outside templates.

Best,
Vicente

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

Nathan Ridge
In reply to this post by lcaminiti

>>> For example, is the following supposed to compile on MSVC10?
>>> #include &lt;boost/mpl/identity.hpp&gt;
>>>
>>> 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).

Regards,
Nate
     

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

lcaminiti
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