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@nhathm
Created April 10, 2017 10:27
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Swift Closure
//: Playground - noun: a place where people can play
// nhathm01247@gmail.com
import Foundation
/** DECLARE A CLOSURE **/
// Declare a variable to hold a closure
var add: (Int, Int) -> Int
// Assign a closure to a variable
add = { (a: Int, b: Int) -> Int in
return a + b
}
// Or combine like this
var sub = { (a: Int, b: Int) -> Int in
return a - b
}
add(1, 2)
sub(1, 2)
// Closure with no params ad no return value
let noLifeClosure: () -> Void = {
print("Programmer have no Life")
}
noLifeClosure()
/** SHORTHAND SYNTAX **/
// Not need return keyword when only have single return statement
add = {(a: Int, b: Int) -> Int in
a + b
}
add(1, 1)
// Remove return type and parameters type
// Because we already declare: var add: (Int, Int) -> Int
add = {(a, b) in
a + b
}
add(9, 2)
// Remove parameters, Swift will refer parameters by number, start from 0:
add = {
$0 + $1
}
add(99, 1)
/*** BUILDIN CLOSURE***/
// SORTED
let ages: [Int] = [1, 6, 99, 2, 5, 3, 57, 28, 19]
var sortedAges = ages.sorted()
// Using custom closure to change sort order
sortedAges = ages.sorted {
$0 > $1
}
// FILTER
let memberAges: [Int] = [1, 6, 12, 17, 19, 22, 35, 43, 57]
let adults = memberAges.filter {
$0 > 17
}
// MAP
// Note 10_000 = 10000, this is Swift way to make easy to read source code
let carSalePrices = [10_000, 34_000, 45_000, 99_000, 103_000, 999_696]
let carPricesInVietNam = carSalePrices.map {
$0 * 200/100
}
// REDUCE
// Note 39_000 = 39000, this is Swift way to make easy to read source code
// Array of tuple (tuple format: (Book name, book quantity, book price)
let books: [(String, Int, Double)] = [("A", 12, 39_000),
("B", 9, 22_000),
("F", 22, 13_000),
("T", 4, 9_000)]
// Using reduce to calculate total prices of all books
let sumPrice = books.reduce(0) {
// Init value (0) or current value + (number of books * price of each book)
$0 + Double($1.1) * $1.2
}
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