> If I have a type Foo with a field that is a pointer to a mutable value, instantiating a Const Foo just means I’m always pointing at the same mutable value, n

> If I have a type Foo with a field that is a pointer to a mutable value, instantiating a Const Foo just means I’m always pointing at the same mutable value, not that I have an unchangeable Foo. yes and that's fine ? for instance how would you encode a graph operation where you want the graph structure to be immutable and the content of the nodes to be variable?