I am trying to adapt one of the boost::asio examples to use c++11 / TR1 libraries where possible. The original code looks like this:
void start_accept() { tcp_connection::pointer new_connection = tcp_connection::create(acceptor_.get_io_service()); acceptor_.async_accept(new_connection->socket(), boost::bind(&tcp_server::handle_accept, this, new_connection, boost::asio::placeholders::error)); } If I replace boost::bind with std::bind as follows:
void start_accept() { tcp_connection::pointer new_connection = tcp_connection::create(acceptor_.get_io_service()); acceptor_.async_accept(new_connection->socket(), std::bind(&tcp_server::handle_accept, this, new_connection, boost::asio::placeholders::error ) ); // std::bind(&tcp_server::handle_accept, this, new_connection, _1 ) ); } I get a large error message, with ends with:
/usr/include/c++/4.4/tr1_impl/functional:1137: error: return-statement with a value, in function returning 'void' I am using gcc version 4.4 with boost version 1.47
I expected boost::bind and std::bind to be interchangeable.
Yes: std::bind should be replaced by lambda For almost all cases, std::bind should be replaced by a lambda expression. It's idiomatic, and results in better code.
Boost. Bind defines placeholders from _1 to _9. These placeholders tell boost::bind() to return a function object that expects as many parameters as the placeholder with the greatest number.
I now have a solution
The problem is that when I first tried to switch to std::bind and std::shared_ptr I was still using the boost::asio::placeholders with std::bind, this resulted in a large amount of template compiler errors, so I then tried to switch piecemeal.
I first tried switching just boost::shared_ptr to std::shared_ptr, this failed because boost::bind will not work with std::shared_ptr with out a specialisation of the template get_pointer<typename T> for std::shared_ptr (see: How to resolve conflict between boost::shared_ptr and using std::shared_ptr?).
After switching to std::shared_ptr I then switched to std::bind, this time using the std::placeholders, (thanks richard) the example code now compiles and works correctly.
In order to use std::bind with boost::asio make sure that std::shared_ptr and the std::placeholders are also used.
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