Inferring the call signature of a lambda or arbitrary callable for “make_function”

Question

In some situations it\'s desirable to be able to type-erase a callable (e.g. function, function pointer, object instance with operator(), lambda, mem_fn

Answer 1

I've come up with a fairly nasty non-library solution, using the fact that lambdas have operator():

template struct remove_class { };
template
struct remove_class { using type = R(A...); };
template
struct remove_class { using type = R(A...); };
template
struct remove_class { using type = R(A...); };
template
struct remove_class { using type = R(A...); };

template
struct get_signature_impl { using type = typename remove_class<
    decltype(&std::remove_reference::type::operator())>::type; };
template
struct get_signature_impl { using type = R(A...); };
template
struct get_signature_impl { using type = R(A...); };
template
struct get_signature_impl { using type = R(A...); };
template using get_signature = typename get_signature_impl::type;

template using make_function_type = std::function>;
template make_function_type make_function(F &&f) {
    return make_function_type(std::forward(f)); }

Any ideas where this can be simplified or improved? Any obvious bugs?