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### Iterator connect token requirements

An iterator connect token is a completion token for completion signature `void(error_code, Iterator)`, where the type `Iterator` is used in the corresponding `async_connect()` function.

##### Examples

A free function as an iterator connect token:

    void connect_handler(
        const boost::system::error_code& ec,
        boost::asio::ip::tcp::resolver::iterator iterator)
    {
      ...
    }

An iterator connect token function object:

    struct connect_handler
    {
      ...
      template <typename Iterator>
      void operator()(
          const boost::system::error_code& ec,
          Iterator iterator)
      {
        ...
      }
      ...
    };

A lambda as an iterator connect token:

    boost::asio::async_connect(...,
        [](const boost::system::error_code& ec,
          boost::asio::ip::tcp::resolver::iterator iterator)
        {
          ...
        });

A non-static class member function adapted to an iterator connect token using `std::bind()`:

    void my_class::connect_handler(
        const boost::system::error_code& ec,
        boost::asio::ip::tcp::resolver::iterator iterator)
    {
      ...
    }
    ...
    boost::asio::async_connect(...,
        std::bind(&my_class::connect_handler,
          this, std::placeholders::_1,
          std::placeholders::_2));

A non-static class member function adapted to an iterator connect token using `boost::bind()`:

    void my_class::connect_handler(
        const boost::system::error_code& ec,
        boost::asio::ip::tcp::resolver::iterator iterator)
    {
      ...
    }
    ...
    boost::asio::async_connect(...,
        boost::bind(&my_class::connect_handler,
          this, boost::asio::placeholders::error,
          boost::asio::placeholders::iterator));

Using use_future as an iterator connect token:

    std::future<boost::asio::ip::tcp::resolver::iterator> f =
      boost::asio::async_connect(..., boost::asio::use_future);
    ...
    try
    {
      boost::asio::ip::tcp::resolver::iterator i = f.get();
      ...
    }
    catch (const system_error& e)
    {
      ...
    }

Using use_awaitable as an iterator connect token:

    boost::asio::awaitable<void> my_coroutine()
    {
      try
      {
        ...
        boost::asio::ip::tcp::resolver::iterator i =
          co_await boost::asio::async_connect(
              ..., boost::asio::use_awaitable);
        ...
      }
      catch (const system_error& e)
      {
        ...
      }
    }