From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2007-05-24 09:15:42
On 5/24/07, Peder Holt <peder.holt_at_[hidden]> wrote:
> 2007/5/24, Minmin Gong <gongminmin_at_[hidden]>:
> [...]
> 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