source url : http://www.boost.org/doc/libs/1_57_0/doc/html/thread/synchronization.html#thread.synchronization.futures

Futures

Overview 

The 4th section say that "Instances can be freely copied and assigned, and boost::shared_future<R>::get() returns a non const reference so that multiple calls to boost::shared_future<R>::get() are safe."

That's just what I am confused about.

Is it one typo ?