Create Swift Dictionary from Array

arrayToDict.swift

/** 
Creates a dictionary with an optional 
entry for every element in an array.
*/
func toDictionary<E, K, V>(
    array:       [E],
    transformer: (element: E) -> (key: K, value: V)?)
    -> Dictionary<K, V>
{
    return array.reduce([:]) {
        (var dict, e) in
        if let (key, value) = transformer(element: e)
        {
            dict[key] = value
        }
        return dict
    }
}

struct Person
{
    let name: String
    let age:  Int
}

let people = [
    Person(name: "Billy", age: 42),
    Person(name: "David", age: 24),
    Person(name: "Maria", age: 99)]

let dictionary = toDictionary(people) { ($0.name, $0.age) }

println(dictionary)
// Prints: [Billy: 42, David: 24, Maria: 99]

This is my suggestion of the extension using the reduce(into:) method of the swift standard library

extension Collection {
    func dictionary<K:Hashable, V>(transform:(_ element: Iterator.Element) -> (key:K, value:V)) -> [K : V] {
        return self.reduce(into: [K : V]()) { (accu, current) in
            let kvp = transform(current)
            accu[kvp.key] = kvp.value
        }
    }
}