Create a Dictionary from any collection (updated from https://gist.github.com/ijoshsmith/0c966b1752b9a5722e23)

CollectionToDictionary.swift

extension Collection {
    func dictionary<K, V>(transform:(_ element: Iterator.Element) -> [K : V]) -> [K : V] {
        var dictionary = [K : V]()
        self.forEach { element in
            for (key, value) in transform(element) {
                dictionary[key] = value
            }
        }
        return dictionary
    }
}

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 dictionary1 = people.dictionary { [$0.name : $0.age] }
//["Billy": 42, "Maria": 99, "David": 24]


// Or, for those who might prefer an initialiser pattern:

extension Dictionary {
    init<C: Collection>(_ collection: C, transform:(_ element: C.Iterator.Element) -> [Key : Value]) {
        self.init()
        collection.forEach { (element) in
            for (k, v) in transform(element) {
                self[k] = v
            }
        }
    }
}

let dictionary2 = Dictionary(people) { [$0.name : $0.age] }
//["Billy": 42, "Maria": 99, "David": 24]