memo

a.rs

let numbers = ["1", "2", "3", "a", "5"];

let only_numbers = numbers.iter()
    .scan((), |_, &item| item.parse::<i32>().ok())
    .collect::<Vec<i32>>(); // [1, 2, 3]

a.swift

let numbers = ["1", "2", "3", "a", "5"]

let onlyNumbers = numbers.flatMap{ Int($0) }    // [1, 2, 3, 5]

var failed = false
let onlyNumbers2 = numbers.reduce(into: [Int]()){ res, item in
    if !failed, let num = Int(item) {
        res.append(num)
    } else {
        failed = true
    }
}   // [1, 2, 3]