Comment by continuational
3 months ago
Thanks!
Yes, you can store the system value (or indeed any other object capability) in a list.
If a function takes in a List[NodeSystem] parameter, then the function can perform side effects through the methods on NodeSystem.
However, if a function takes in a List[T] where T is a type parameter, then that is not enough to perform side effects, even if that function is later called with a List[NodeSystem] argument. There is no way for the function to access the methods of the concrete type of T.
Hence, you can tell whether or not a function may have side effects from the function signature alone.
Realistically, in a bigger project, you might have a NodeSystem type n layers deep buried.
E.g. you just grabbed a hypothetical canvas dependency, which has a Canvas. Can you tell if it does any form of IO or not?
Only capability type can have fields containing other (concrete) capability types.
If Canvas contains NodeSystem, then Canvas must be a capability type itself.