can someone explain this auto type? (when doing `f...

# announcements

[Andrew Gazelka]

can someone explain this auto type? (when doing flowOf(1, 1.0, 2, 2.0))… don’t understand the &

[elizarov]

& here reads as and. The types here are comparable to any type that is Double and Int at the same time (such types don’t exist, but compiler does not check that) and extend Number.

[Marc Knaup]

Why doesn't it just resolve to Number?

[diesieben07]

Because Comparable<Double & Int> is more precise than Number

[Marc Knaup]

But Double & Int is impossible? A type cannot be both at once.
Comparable<Double | Int> would make sense to me.

[diesieben07]

It's a union type, it can be either double or int.

[karelpeeters]

Think about actually using the interface: if I want to call compareTo I need to give sometime that is both an Int and a Double for it to work. Obviously that's impossible, but the type system doesn't know that.

[Marc Knaup]

@diesieben07 my example is union. The initial one is intersection

[diesieben07]

True. I need to think about this more 😄

[Marc Knaup]

@karelpeeters as far as I understand the type system does know (otherwise type inference would never work), tots just that the compiler doesn't care.
There was an article on intersection types in inference and why they're different from actual types but I can't find it anymore.

[karelpeeters]

Okay, but that doesn't change what I said: Int & Double does make sense, Int | Double wouldn't.

[Marc Knaup]

Ah, now I see it. I've always assumed that Java's Number is Comparable but it isn't.

So the initial type basically reads

this is a Number which is Comparable but you can't actually use generic elements of Comparable because the possible type arguments are disjoint up to but excluding Any Number

(out may work as Any Number but Comparable has no type arguments in out position)

[karelpeeters]

Not sure about "up to but including", Any doesn't work either. Nothing does simple smile But yeah, that what it means.

[Marc Knaup]

Yeah it depends on the projection. I've just updated my message :)

[Hullaballoonatic]

please give & syntax for type parameters instead of where syntax, JB!

[elizarov]

Do you use it often? Just remember, that are so few ascii characters — each one is precious.