### Resolve token requirements

A resolve token is a completion token for completion signature `void(error_code, ip::basic_resolver_results<InternetProtocol>)`, for a specified `InternetProtocol`.

##### Examples

A free function as a resolve token:

    void resolve_handler(
        const asio::error_code& ec,
        asio::ip::tcp::resolver::results_type results)
    {
      ...
    }

A resolve token function object:

    struct resolve_handler
    {
      ...
      void operator()(
          const asio::error_code& ec,
          asio::ip::tcp::resolver::results_type results)
      {
        ...
      }
      ...
    };

A lambda as a resolve token:

    resolver.async_resolve(...,
        [](const asio::error_code& ec,
          asio::ip::tcp::resolver::results_type results)
        {
          ...
        });

A non-static class member function adapted to a resolve token using `std::bind()`:

    void my_class::resolve_handler(
        const asio::error_code& ec,
        asio::ip::tcp::resolver::results_type results)
    {
      ...
    }
    ...
    resolver.async_resolve(...,
        std::bind(&my_class::resolve_handler,
          this, std::placeholders::_1,
          std::placeholders::_2));

A non-static class member function adapted to a resolve token using `boost::bind()`:

    void my_class::resolve_handler(
        const asio::error_code& ec,
        asio::ip::tcp::resolver::results_type results)
    {
      ...
    }
    ...
    resolver.async_resolve(...,
        boost::bind(&my_class::resolve_handler,
          this, asio::placeholders::error,
          asio::placeholders::results));

Using use_future as a resolve token:

    std::future<asio::ip::tcp::resolver::results_type> f =
      resolver.async_resolve(..., asio::use_future);
    ...
    try
    {
      asio::ip::tcp::resolver::results_type r = f.get();
      ...
    }
    catch (const system_error& e)
    {
      ...
    }

Using use_awaitable as a resolve token:

    asio::awaitable<void> my_coroutine()
    {
      try
      {
        ...
        asio::ip::tcp::resolver::results_type r =
          co_await resolver.async_resolve(
              ..., asio::use_awaitable);
        ...
      }
      catch (const system_error& e)
      {
        ...
      }
    }