Template:cpp/memory/auto ptr/auto ptr ref note

The constructor and the copy assignment operator from is provided to allow copy-constructing and assigning std from nameless temporaries. Since its copy constructor and copy assignment operator take the argument as non-const reference, they cannot bind rvalue arguments directly. However, a can be executed (which releases the original ), followed by a call to the constructor or copy-assignment operator that take  by value. This is an early implementation of move semantics.