2 summary::a reference to the copy of a value
6 A Ref instance is an object with a single slot named 'value' that serves as a holder of an object.
7 RefCopy, in difference to Ref, returns only copies of the value when next is called.
8 This can be useful when the original is to be kept unchanged.
10 see link::Classes/Ref:: for other methods.
18 b.put(0, 100); // modify b