[cogman10]

Immutable from a mutable is just as implausible. You cannot remove a method from a subtype which results in mutating methods being disabled through other means (like throwing exceptions).

This is also a violation of LSP and the open close principle.

Consider a `List` with an `add` function. What would you do with that `add` function to make an `ImmutableList` subtype?

[aatd86]

Ah I see. Why throw exceptions? They could just be noop depending on the typestate?

But still it doesn't look very nice in practice. I think that in that case, it does make much more sense for a mutable type to be a subtype of the immutable one.

The immutable threw me off track. It's just that the supertype would lack mutation operations. (in a sense immutable would be the default for every type).

Thank you.