Is it safe to call non-const member functions for rvalue objects?

Question

While reading about multithreading in C++11, I noticed that some tutorials do this:

std::thread(print_message, "Hello").detach();

// instead of...

std::thread t(print_message, "Hello");
t.detach();

My questions are:

1. In general, is it safe to call non-const member functions for temporary (rvalue) objects?
2. In particular, is it safe to do so for a C++11 std::thread?

Answer 1

1. Yes: the non-const function gets executed while the object is still alive, so there is no problem.
2. Yes: std::thread behaves as any other type.

Answer 2

To elaborate more on the second question, the temporary std::thread object behaves like any other temporary object:

It is destroyed after the full expression it is bound to is evaluated, which means the destructor is always called after the .detach() call - std::terminate() is not called.

Answer 3

In answer to question 1: You are not allowed to modify anonymous temporaries of "non-class" type (i.e.. built-in types). You are, however, allowed to call non-const member functions on anonymous temporaries of "class" type. See Section 3.10.10 in C++ ISO/IEC 14882:1998 standard.