Can streams be copied?

No, it is not possible. Streams (classes like std::thread in C++) do not have copy semantics. This is because a thread represents a unique resource of the operating system associated with executing code. Copying such a resource is impossible, as each thread has its own stack, registers, and execution state. Attempting to copy a std::thread object will result in a compile-time error or undefined behavior.

However, threads can be moved:

#include <thread>
#include <iostream>
#include <utility> // for std::move

void worker() {
    std::cout << "Worker thread executing.\n";
}

int main() {
    std::thread t1(worker); // Create a thread

    //std::thread t2 = t1; // Compile error: copying not allowed

    std::thread t2 = std::move(t1); // Move the thread

    // t1 is now in a valid but unspecified state (not representing an active thread)

    if (t2.joinable()) {
        t2.join(); // Wait for the moved thread to finish
    }

    return 0;
}

The ability to move allows ownership of the thread to be transferred between objects, which is useful in various resource management scenarios.