What is [this, self] before handler assignment means in Boost library asio example?
boost, boost-asio, c++, c++11
Solution
That is the capture-list of the lambda. It is capturing the variable `this` (pointer) and the variable `self` declared one line above.
[...](...){...}
// A B C
The above is simplified syntax for the lambda in your code. `A` is the capture-list mentioned above (used to "capture" variables from the current scope). `B` is the argument list (just like in a function) and `C` is the body (again, like a function).
Problem
I have never seen such syntax before "[this, self]", I used to program C and did a bit with C++, and now learning C++11 and Boost library, the compiler is happy with, but I can't figure out how it works and what it does. ``` void do_read() { auto self(shared_from_this()); socket_.async_read_some(boost::asio::buffer(data_, max_length), [this, self](boost::system::error_code ec, std::size_t length) ---------^ { if (!ec) { do_write(length); } }); } ``` It comes from Boost library Async Echo server example in this link