[swift-users] Generic factory method and type inference

Rudolf Adamkovič salutis at me.com
Thu Mar 17 08:58:30 CDT 2016

Hello there!

I have the following class with a generic factory method:

final class Something<T> {
    let value: T
    init(initial: T) {
        value = initial

extension Something {
    class func zip<A, B>(a: A, _ b: B) -> Something<(A, B)> {
        let initial = (a, b)
        return Something<(A, B)>(initial: initial)

How come I can’t call zip without explicitly specifying return type?

// ERROR: Cannot invoke `zip` with an argument list of type `(Int, Int)`
let y = Something.zip(1, 2)

// OK: Works but it’s unacceptable to require this on caller's side
let x = Something<(Int, Int)>.zip(1, 2)

Thank you for your time!

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