[Olreich]

Const only saves you most of the time if you have a “const” all the way down the type structure. 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.

Const support in languages never makes all modifications to data accessed through the variable locked out, just the top level, which makes it much more difficult to ensure that the assumptions about immutability hold without constantly doing deep copies or having to double and triple check that your Const definitions are correct.

Const often leads to a false sense of security.

[jcelerier]

> 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?