Swift Functional Programming: Map

Map.swift

// Swift Functional Programming: Map
//
// By Miguel Fermin on 2016.01.28
//
// Reference: https://www.weheartswift.com/higher-order-functions-map-filter-reduce-and-more/

import UIKit


// The map method solves the problem of transforming the elements of an array using a function.
//
// It transforms [ x1, x2, ... , xn].map(f) to [f(x1), f(x2), ... , f(xn)]

// Task: Convert an array of Ints into an array of Strings with each number appended by a dollar sign '$'

let nums = [20, 40, 60, 80, 100]

// The old way
var result0 = [String]()
for num in nums {
    result0.append("$\(num)")
}
result0

// Using Array's map method.
let result1 = nums.map {"$\($0)"}
// result1 equals ["$20", "$40", "$60", "$80", "$100"]

// In Swift map is declared as a method on the Array class with signature:
//
//      func map<U>(transform: (T) -> U) -> U[]
//
// That just means that it receives a function named transform that maps the array element
// type T to a new type U and returns an array of U