Yes, but the same could be done in C: just make several compilation units, one per Canvas (or put several canvas in the same files, if they are small enough).

Yes, but the same could be done in C: just make several compilation units, one per Canvas (or put several canvas in the same files, if they are small enough). Now if you thought of using a Canvas without determining a which one before hand, then you need subtype polymorphism, a much more significant feature, of which I do see the benefits.