在Swift中展平数组数组

在Swift中有一个对应的平台在Scala，Xtend，Groovy，Ruby和co？

var aofa = [[1,2,3],[4],[5,6,7,8,9]]
aofa.flatten() // shall deliver [1,3,4,5,9]

当然我可以使用减少为那，但是那种吸

var flattened = aofa.reduce(Int[]()){
    a,i in var b : Int[] = a
    b.extend(i)
    return b
}

Swift 3.0

减少：

let numbers = [[1,9]]
let reduced = numbers.reduce([],+)

flatMap：

let numbers = [[1,9]]
let flattened = numbers.flatMap { $0 }

加入：

let numbers = [[1,9]]
let joined = Array(numbers.joined())