Thanks for answering. As I said in another comment (in reply to another tsimionescu who suspected that's what you meant), I maintain that this is a compile time

Thanks for answering. As I said in another comment (in reply to another tsimionescu who suspected that's what you meant), I maintain that this is a compile time error. Yes, one usage is to panic if the contents of the enum is not what you expect, in which case an unexpected type causes a runtime error. But that is the programmer choosing to deal with it way. Fundamentally in the language, mismatching type is a compile time error. In many situations it's feasible to exhaustively match and deal with all possible cases of an enum (which then causes a compile time error if you try to reference one of the other inner types from within the "wrong" case). Where one particular case is expected, you can often ensure through the type system that this case is the only possibility by using that individual type directly rather than passing that enum around. In some situations its not feasible or it is feasible but the extra faff isn't worth the reward - but even then I don't think it justifies saying that the type confusion is detected in runtime in a comparison of languages.