shared_lock& operator=( shared_lock&& other );
Move assignment operator. Replaces the contents with those of
other using move semantics.
If, prior to this call, *this has an associated mutex ((mutex() returns a non-null pointer) and has acquired ownership of it (owns() returns true), the mutex is unlocked by calling unlock_shared().
After this call,
other has no associated mutex.
|other||-|| another |
 Return value