Rename {super,sub} set methods to clearly indicate relation of operands

[straight-shoota]

I just realized that methods like Set#subset? apply in exactly the opposite direction to what I might expect.
I would probably read a predicate method subset?(b) as "is b a subset? (of the receiver)", i.e. b ⊂ a But instead a.subset?(b) returns true if a ⊂ b.

These semantics are the same as in Ruby. I suspect they have it that way to have the same operand relation as with the comparison operators. But it's really confusing. When reading the code, you can't beyond doubt recognize which way it is.

So I'm proposing to rename these methods to a differnt, less ambiguous name. Adding a simple _of suffix would fix this. a.subset_of?(b) clearly means a ⊂ b.

• Set#subset? => Set#subset_of?
• Set#proper_subset? => Set#Proper_subset_of?
• Set#superset? => Set#superset_of?
• Set#proper_superset? => Set#proper_superset_of?

This also affects proposed similar methods for Hash (see #7500 (comment))

[asterite]

Bang methods apply to the receiver. a.includes?(b) means "does a include b"? So a.subset?(b) naturally means "is a a subset of b?". So I don't this needs to change.

That said, adding the "of" suffix makes it a bit more readable.

[straight-shoota]

I don't follow how you see a relation to bang methods. This is not about question mark representing nilable methods. Even if there is one, it's not obvious, which supports the argument that the API should be more explicit.

These are all predicate methods. And as such, either way to read the relation between receiver and arg is possible. And as I mentioned above, I intuitively read a.subset?(b) as asking a: "is b a subset?"
Removing this ambiguity is a good improvement.

[asterite]

Oh, sorry, I meant "question method".

And as I mentioned above, I intuitively read a.subset?(b) as asking a: "is b a subset?"

That's the thing. Whenever there's a.method?(b) it means "Is 'a method? b'" true? In the case of a.subset?(b) it means "is a a subset of b"? In the case of a.includes?(b)" is "does 'a includes b' hold true?". aalways appears **before**b` in the sentence.

A question method is always asking "Are you ...?" or "Do you ...?". It never asks something about the argument.

That said, I think the "of" suffix makes this a bit clearer.