Is it possible to figure out the parameter type and return type of a lambda?

Question

Given a lambda, is it possible to figure out it\'s parameter type and return type? If yes, how?

Basically, I want lambda_traits which can be used in fol

Answer 1

Though I'm not sure this is strictly standard conforming, ideone compiled the following code:

template< class > struct mem_type;

template< class C, class T > struct mem_type< T C::* > {
  typedef T type;
};

template< class T > struct lambda_func_type {
  typedef typename mem_type< decltype( &T::operator() ) >::type type;
};

int main() {
  auto l = [](int i) { return long(i); };
  typedef lambda_func_type< decltype(l) >::type T;
  static_assert( std::is_same< T, long( int )const >::value, "" );
}

However, this provides only the function type, so the result and parameter types have to be extracted from it. If you can use boost::function_traits, result_type and arg1_type will meet the purpose. Since ideone seems not to provide boost in C++11 mode, I couldn't post the actual code, sorry.