Q: Is it possible to add __is to a type?

[Andre-LA]

I'm a bit lost in this problem, here's an example:

local record Foo
	type X = {string, number, boolean} -- tuple structure, so I can init with {'a', 1, true}

	record Y
		-- without this we get "cannot discriminate a union between multiple table types: X | Y" (fair!)
		where type(self.z) == 'number'
		z: number
	end

	type A = X | Y --> cannot mix table types with and without __is metamethod: X | Y
	-- so.. how could we add __is to X? I tried record X is {string, number, boolean}, but that's not allowed
end

For now, I'll see if I can do other data-strucutre

[hishamhm]

I tried record X is {string, number, boolean}, but that's not allowed

I think the easiest way would be to extend the language to allow this.

Now that instead of arrayrecord types we have the array type as an interface of the record, implementing this should be easier too. (There might still be some special-casing left in the compiler for records-as-arrays but it's way less "special" than before).

For maps, there's a conflict between string keys and record field names; that would take extra logic to check for conflicts.