How to perform map+filter in one command. Thanks to @nxsteveo @a2 & @nicklookwood

flatmap.swift

import Foundation

let a  = [1,2,3,4,5]
let b =  a.flatMap{ (i) -> (Int?) in
    if i % 2 == 0 {
        return i
    } else {
        return nil
    }
}

func foo(bar: Int) -> Int? {
    if bar % 2 == 0 {
        return bar
    } else {
        return nil
    }
}

let c = a.flatMap{foo(bar: $0)}

let d = a.filter{ i in
    i % 2 == 0
}

func pippo(text: String) -> Int? {
    if text.isEmpty {
        return nil
    } else {
        return text.characters.count
    }
}

let e = ["", "dog", "cat"].flatMap{pippo(text: String($0))}