Move-assign
a basic_writable_pipe
from another.
basic_writable_pipe & operator=( basic_writable_pipe && other);
This assignment operator moves a pipe from one object to another.
The other basic_writable_pipe
object
from which the move will occur.
Following the move, the moved-from object is in the same state as if constructed
using the basic_writable_pipe(const executor_type&)
constructor.