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### Composed connect handler requirements

A composed connect handler must meet the requirements for a handler. A value `h` of a composed connect handler class should work correctly in the expression `h(ec, i)`, where `ec` is an lvalue of type `const error_code` and `i` is an lvalue of the type `Iterator` used in the corresponding `connect()` or async_connect()` function.

##### Examples

A free function as a composed connect handler:

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

A composed connect handler function object:

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

A non-static class member function adapted to a composed connect handler using `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));