Using flatMap to convert a list of mixed nils and values into a list of non-optional values

flatMap.swift

let numbers = [
    "one",
    "2",
    "0x3",
    "42",
]

// This will run the function on all values and only keep the ones that are not nil:
let parsedNumbers = numbers.flatMap { Int($0, radix: 10) }
// [2, 42]

// flatMap also works directly on optionals so you don't have to check for nil before:
let doubled = Int("123", radix: 10).flatMap { $0 * 2 }
// 246