lambda traits inconsistency across C++0x compilers
- by Sumant
I observed some inconsistency between two compilers (g++ 4.5, VS2010 RC) in the way they match lambdas with partial specializations of class templates. I was trying to implement something like boost::function_types for lambdas to extract type traits. Check this for more details.
In g++ 4.5, the type of the operator() of a lambda appears to be like that of a free standing function (R (*)(...)) whereas in VS2010 RC, it appears to be like that of a member function (R (C::*)(...)). So the question is are compiler writers free to interpret any way they want? If not, which compiler is correct? See the details below.
template <typename T>
struct function_traits
: function_traits<decltype(&T::operator())>
{
// This generic template is instantiated on both the compilers as expected.
};
template <typename R, typename C>
struct function_traits<R (C::*)() const> { // inherits from this one on VS2010 RC
typedef R result_type;
};
template <typename R>
struct function_traits<R (*)()> { // // inherits from this one g++ 4.5
typedef R result_type;
};
int main(void) {
auto lambda = []{};
function_traits<decltype(lambda)>::result_type *r; // void *
}
This program compiles on both g++ 4.5 and VS2010 but the function_traits that are instantiated are different as noted in the code.
