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        An accept handler must meet the requirements for a handler.
        A value h of an accept handler
        class should work correctly in the expression h(ec),
        where ec is an lvalue of
        type const error_code.
      
A free function as an accept handler:
void accept_handler( const asio::error_code& ec) { ... }
An accept handler function object:
struct accept_handler { ... void operator()( const asio::error_code& ec) { ... } ... };
        A non-static class member function adapted to an accept handler using bind():
      
void my_class::accept_handler( const asio::error_code& ec) { ... } ... acceptor.async_accept(..., boost::bind(&my_class::accept_handler, this, asio::placeholders::error));