std::unique_ptr baby

Captures in lambdas are const by default. So in order to
be able to move from them, we mark the entire lambda
as mutable. Thus, member variables in our closure object
are no longer const. Also, using a variable multiple times
on the same line and one of the uses is modifying the
variable is a no-no. Extract the pointer out of the unique_ptr
before performing modifying operation.

Author: MarekKnapek

echo_server.cpp

@@ -27,20 +27,22 @@ void handle_request(const std::error_code& error, tcp::socket socket) {
         return;
     }
 
-    auto request = std::make_shared<Request>(std::move(socket));
+    auto request = std::make_unique<Request>(std::move(socket));
 
     printf("Accepted connection\n");
 
-    asio::async_read_until(request->socket, request->buffer, '\n',
-        [request](const auto &error, size_t bytes_transferred) {
+    auto req = request.get();
+    asio::async_read_until(req->socket, req->buffer, '\n',
+        [request = std::move(request)](const auto &error, size_t bytes_transferred) mutable {
             if (error) {
                 const auto &msg = error.message();
                 printf("Error while reading: %s\n", msg.c_str());
                 return;
             }
             printf("Received %zu bytes\n", bytes_transferred);
-            asio::async_write(request->socket, request->buffer,
-                [request](const auto &error, size_t bytes_transferred) {
+            auto req = request.get();
+            asio::async_write(req->socket, req->buffer,
+                [request = std::move(request)](const auto &error, size_t bytes_transferred) mutable {
                     if (error) {
                         const auto &msg = error.message();
                         printf("Error while writing: %s\n", msg.c_str());