An extension to the Collection Type to create a dictionary using a transform closure.

Collection-to-Dict.swift

extension Collection {
    // Create a Dictionary from a collection using a transformer.
    // The transformer function takes an element from the collection and returns a tuple
    // with the key/value pair.
    func dictionary<K, V>(transform:(_ element: Iterator.Element) -> (K, V)) -> [K : V] {
        var dictionary = [K : V]()
        self.forEach { element in
            let (key, value) = transform(element)
            dictionary[key] = value
        }
        return dictionary
    }
}


let col = [1,2,3,4]

let powers = col.dictionary { (x) -> (Int, Int) in
    (x, x*x)
}