// Return io_context* from io_context::executor_type
inline
net::io_context*
get_io_context_impl(
    net::io_context::executor_type const& ex)
{
    return &ex.context();
}

// Return io_context* from net::executor
template<class T
    , class = typename std::enable_if_t<
        std::is_same<T, net::executor>::value>::type>
net::io_context*
get_io_context_impl(
    T const& ex)
{
    auto p = ex.target<
        net::io_context::executor_type>();
    if(! p)
        return nullptr;
    return &p->context();
}

template<class T>
net::io_context*
get_io_context_impl(T const&)
{
    return nullptr;
}

template<class T>
net::io_context*
get_io_context_impl(T& t, std::true_type)
{
    return get_io_context_impl(
        t.get_executor());
}

template<class T>
net::io_context*
get_io_context_impl(T&, std::false_type)
{
    return nullptr;
}

template<class Executor>
net::io_context*
get_io_context(net::strand<Executor> const& strand)
{
    return get_io_context_impl(
        strand.get_inner_executor());
}

template<class T>
net::io_context*
get_io_context(T& t)
{
    return get_io_context_impl(t,
        has_get_executor<T>{});
}