I have a client program written by someone who is no longer available. The client program can send a message via async_write to server, but when the server responded back, the client boost::asio::async_read got an error of Operation cancelled. Searching from the Internet, it said the program was caused mostly by using this which should be fixed by using shared_from_this(). But in my client program it does not use this or shared_from_this, could someone explains if it uses some default format implies to this or shared_from_this in following example? (What (=) means, some kind of lambda function?)

boost::asio::async_read(this->socket, boost::asio::buffer(this->messageHeader),
[=](const boost::system::error_code &error, const uint32_t length) {this->readMessageHeader(error, length);});