> I don't believe it is possible (or even makes sense) to completely avoid illegal/invalid objects and structures, and a cheap way to mark these are nil pointer

> I don't believe it is possible (or even makes sense) to completely avoid illegal/invalid objects and structures, and a cheap way to mark these are nil pointers Obviously we should be able to represent objects with possibly invalid state, but rather than allowing a "possibly invalid value" as a legitimate member of a huge number of types, which is what nil/null permits, the possible invalidity should be it's own type, like a MaybeInvalid<T>. Even languages that bake null checking into the type system are doing this, and then just inserting implicit conversions to/from such a type.