On 5/24/07, Peder Holt <peder.holt@gmail.com> wrote:

2007/5/24, Minmin Gong <gongminmin@yeah.net>: [...] On GCC we use the native typeof mechanism, so your code is actually translated into this:

int main() { std::vector<int> v; typedef typeof(boost::type_of::ensure_obj(v))::type type; }

The simpler: typedef typeof(v)::type type;

fails to compile as well, so this is a shortcomming in the compiler.

Well, vector has no 'type' type. Anyways, It fail)s for 'iterator' too: std::vector<int> v; typedef typeof(int)::iterator type;

Unfortunately there is little we can do to fix this in Boost.Typeof.

This works though (at least with gcc 4.1.2): #include <vector> template<typename T> struct identity { typedef T type; }; int main() { std::vector<int> v; typedef identity<typeof(v)>::type::iterator type; } So BOOST_TYPEOF could include 'identity' in its expansion. It might fail with more complex expression as I heard that gcc doesn't like much typeof in template parameters (but never tested it). gpd

On 5/24/07, Arkadiy Vertleyb <vertleyb@hotmail.com> wrote:

"Giovanni Piero Deretta" <gpderetta@gmail.com> wrote

...

This works though (at least with gcc 4.1.2):

#include <vector>

template<typename T> struct identity { typedef T type; };

int main() { std::vector<int> v; typedef identity<typeof(v)>::type::iterator type; }

So BOOST_TYPEOF could include 'identity' in its expansion.

Working around the problem by _complicating_ the expression inside typeof is not a way I would go. It then may fail in another contexts, where it didn't fail before.

Agreed, In fact I said myself that the 'simple' solution could break with more complex expressions.

This is clearly a compiler bug, and needs to be addressed by the compiler developers.

Well, boost as plenty of workarounds for broken compilers, so I do not think this matter much. Even if gcc developers fixthis, older releases will be still broken. Anyways, IIRC next release might support decltype, so the issue is moot. gpd