My first question is about terminology used. I get why the code example works, but the description I quoted says the reverse (i.e. "Animal is a subtype of Cat", and "Animal is a supertype of Thing"). I assume that it's an error then.
Thx for the answer to the second question :). I think my mind put an additional "by" in that sentence and got confused.
> I ask because I'm not sure about the grammar aspect, and in my native language (Polish) we have a few ambiguities like that, which I sometimes jokingly write down with an arrow, e.g. "A can be ---substitutes for--> B" or "A can be <--substituted for-- B", to make it damn explicit which direction the word works.
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I think it's confusing for 2 reasons: passive voice and prepositions.
1) Passive voice - instead of saying A substitutes for B (active voice) it says A can be substituted for B (passive voice.)
2) Prepositions - "be substituted" can collocate with "for" or "by" with the opposite meaning!
A <-- can be substituted by <-- B (use B where you would expect A)
A --> can be substituted for --> B (use A where you would expect B)
Yes I think he has made a mistake there. He did get it right earlier in the article he says "This makes Cat a subtype of Animal. That means that all Cats are Animals, but not all Animals are Cats."
Thx for the answer to the second question :). I think my mind put an additional "by" in that sentence and got confused.