cpp/experimental/ranges/iterator/Writable

The concept specifies the requirements for writing a value whose type and value category are encoded by  into an iterator 's referenced object.

Let be an expression such that  is, and  be a dereferenceable object of type , then  is satisfied only if:
 * If is satisfied, then  after any above assignment is equal to the value of  before the assignment.

is not required to be dereferenceable after evaluating any of the assignment expressions above. If is an xvalue, the resulting state of the object it denotes is valid but unspecified.