I would personally treat a type like "table" to be an interface. So anything could be a table, as long as you could use it like a table.
Your example of something that claims to be an array but gives you trouble if you treat it like an array strikes me as more an issue with that particular bad implementation...
Interesting question though: what would treating types like interfaces look like from an Arc point of view? I'll have to think about that one :)
Update: I wrote this before I saw Pauan's comment :)
:) In that rails example scopes don't claim to be arrays. Hmm, perhaps it's just that printing them on the console is confusing. Perhaps other forms of overloading aren't so bad, and perhaps I can even handle the console with a slightly different mindset - not judging values by how they print.
