Question

Say you have the following:

foo(x: String)(y: Int): Int
foo(x: String)(y: Double): Int

Scala does not allow such expression. As far as I can see, the reason for this is that foo(“asdf”) does not have a well defined type (it’s either Int => Int or Double => Int).

Is there a reason why such “polytyped” functions should not be allowed?

Answer 1

Overloading resolution in Scala takes only the first parameter list into account. That’s why alternatives must differ already in this list. There’s a good reason for this: We can then use the resolved function’s type to infer the type of subsequent arguments. This enables idioms like:

xs.corresponds(ys) { (x, y) => x < y }

Note that here we need to know the type of corresponds in order to infer the types of x and y. It would be a shame to have this break down when corresponds is overloaded.