Swift job interview idea: implement Dictionary.map

gistfile1.md

Swift job interview idea: implement Dictionary.map

https://twitter.com/narfdotpl/status/558348210079809536

First try on a piece of paper

extension Dictionary {
    func map<A: Hashable, B>(f: (Hmm.Key, Hmm.Value) -> (A, B)) -> [A: B] {
        var d: [A: B] = [:]

        for (k, v) in map(self, f) {
            d[k] = v
        }

        return d
    }
}

• I thought Hashable is needed. Turns out it's not.
• I didn't know how to reference original key and value types. Turns out they're just Key and Value.
• I didn't see recursion in map(self, f). :p

With a compiler

extension Dictionary {
    func map<A, B>(f: (Element) -> (A, B)) -> [A: B] {
        var d: [A: B] = [:]

        for (k, v) in Swift.map(self, f) {
            d[k] = v
        }

        return d
    }
}