> but can't an object be considered immutable when all its fields are immutable and all its member functions (but the constructor perhaps) are pure?
How exactly do you expect to track this accurately without integrating it into the type system?
It's not an issue of whether or not the field itself is assignable, but whether or not the type that it points to is mutable. This becomes much more difficult to determine when generics are involved. This sort of type level knowledge for generics would make it hard to staple onto an existing type system. Even if you did, you would likely end up with a lot of code duplication as you would need two forms of types, immutable and mutable, e.g. `ImmVector` and `MutVector`, `ImmMap` and `MutMap`, `ImmMyObject` and `MutMyObject`, etc.
To make this more ergonomic, Skip has a mode based mutability model, where the mutability is determined not at the class declaration, but rather at the type annotation/object instantiation. So we would then have `Vector` and `mutable Vector`, two modes of the same class.
> but can't an object be considered immutable when all its fields are immutable and all its member functions (but the constructor perhaps) are pure?
How exactly do you expect to track this accurately without integrating it into the type system? It's not an issue of whether or not the field itself is assignable, but whether or not the type that it points to is mutable. This becomes much more difficult to determine when generics are involved. This sort of type level knowledge for generics would make it hard to staple onto an existing type system. Even if you did, you would likely end up with a lot of code duplication as you would need two forms of types, immutable and mutable, e.g. `ImmVector` and `MutVector`, `ImmMap` and `MutMap`, `ImmMyObject` and `MutMyObject`, etc. To make this more ergonomic, Skip has a mode based mutability model, where the mutability is determined not at the class declaration, but rather at the type annotation/object instantiation. So we would then have `Vector` and `mutable Vector`, two modes of the same class.
You can read more here: http://skiplang.com/blog/2018/04/10/understanding-mutability...