Why Does Passing a Class Object by Reference to std::thread Still Trigger the Copy Constructor?

std::thread Passing by Reference Invokes Copy Constructor

Issue:

When passing an object of class Log to an std::thread by reference, a compiler error occurs, despite expectations that reference passing should bypass the copy constructor. Conversely, passing the object by pointer resolves the issue.

Explanation:

The underlying reason for this behavior is that std::thread requires its arguments to be passed by value. Passing by reference, as in Log &logger, has the same effect as passing a pointer, i.e., it still requires a copy constructor to generate a copy of the object to be passed to the thread.

Solution:

To regain reference semantics, sử dụng std::reference_wrapper:

std::thread newThread(session, &sock, std::ref(logger));

Note:

1. Ensure that the lifetime of the referenced object (logger in this case) exceeds that of the thread.
2. In the provided code, Log's copy constructor is private, preventing the creation of additional copies.

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