‏map و filter الكسولان

let nums = Array(1...6)
let result = nums
    .filter { $0 % 2 == 0 }  // builds [2, 4, 6]
    .map { $0 * 10 }         // builds [20, 40, 60]
print(result)  // [20, 40, 60]

let nums = Array(1...6)
let result = nums.lazy
    .filter { $0 % 2 == 0 }
    .map { $0 * 10 }
print(Array(result))  // [20, 40, 60]

let out = [1, 2, 3].lazy
    .filter { n -> Bool in print("filter \(n)"); return n > 1 }
    .map   { n -> Int  in print("map \(n)");    return n }
print(Array(out))  // filter 1, filter 2, map 2, filter 3, map 3 -> [2, 3]

let nums = Array(1...1_000_000)
let hit = nums.lazy.map { $0 + 1 }.first { $0 > 5 }
print(hit!)  // 6  -- only a handful of elements processed

let squares = (1...).lazy.map { $0 * $0 }
print(Array(squares.prefix(5)))  // [1, 4, 9, 16, 25]

var transforms = 0
let result = Array(1...100).lazy
    .map { (n: Int) -> Int in transforms += 1; return n * 2 }
    .prefix(3)
_ = Array(result)
print(transforms)  // 3, not 100

let raw = ["1", "x", "3", "y", "5"]
let first = raw.lazy.compactMap { Int($0) }.first
print(first!)  // 1

let r = Array(1...20).lazy
    .filter { $0 % 2 == 0 }
    .map { $0 * $0 }
    .filter { $0 > 50 }
print(Array(r))  // [64, 100, 144, 196, 256, 324, 400]

let big = Array(1...10_000)
let sample = Array(big.lazy.filter { $0 % 1000 == 0 })
print(sample)  // [1000, 2000, ... 10000]