inline
net::io_context*
get_io_context(net::io_context& ioc)
{
    return &ioc;
}

inline
net::io_context*
get_io_context(net::io_context::executor_type const& ex)
{
    return &ex.context();
}

inline
net::io_context*
get_io_context(net::strand<
    net::io_context::executor_type> const& ex)
{
    return &ex.get_inner_executor().context();
}

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

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

inline
net::io_context*
get_io_context(...)
{
    return nullptr;
}

//------------------------------------------------------------------------------

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

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

// Returns the io_context*, or nullptr, for any object.
template<class T>
net::io_context*
get_io_context(T& t)
{
    return get_io_context_impl(t,
        has_get_executor<T>{});
}