Extract template class default parameters

Is there a way to extract a template class' default parameters only knowing the unspecialized template class at compile time?

I know how to extract an instantiated template class' parameters, like this:

// Just an example class for the demonstration
template<class A, class B=void>
struct example {};

// Template parameters storage class
template<class...An>
struct args;

// MPL utility that extracts the template arguments from a template class
template<class C>
struct get_args
{
    typedef args<> type;
};
template<template<class...> class C, class...An>
struct get_args< C<An...> >
{
    typedef args<An...> type;
};

// And the assertion
static_assert(
    std::is_same
    <    args<int,void>,
         get_args< example<int> >::type
    >::value,
    "Check this out"
);

Now what I would like to know is if decltype or anything else could be used to retrieve the default template parameters only from the unspecialized template class:

// MPL utility that extract template default arguments from a template class
template<template<class...> class C>
struct get_default_args
{
    typedef /* what goes here? */ type;
};

// And the assertion
static_assert(
    std::is_same
    <    args<void>,
         get_default_args< example >::type
    >::value,
    "Check this out"
);

For now, I only figured out how to extract the number of parameters of a template class, not their default value:

namespace detail {
    template< template<class> class >
    boost::mpl::size_t<1> deduce_nb_args();
    template< template<class,class> class >
    boost::mpl::size_t<2> deduce_nb_args();
    template< template<class,class,class> class >
    boost::mpl::size_t<3> deduce_nb_args();
    /* ... and so on ... */
}

// MPL utility that extract the number of template arguments of a template class
template<template<class...> class C>
struct get_nb_args :
  decltype(detail::deduce_nb_args<C>()) {};

// And the assertion
static_assert(
    get_nb_args< example >::value == 2,
    "Check this out"
);