closures.swift

// FUNCTION WITH NO NAME

// SPECIAL CASES OF CLOSURE

//let sum = { (a: Int, b: Int) -> Int in
//    return a + b
//}

//let result = sum(4, 2)

// "CLOSE OVER"

// ACCESS, STORE & MANIPULATE SURROUNDING CONTEXT

// VALUES CAPTURED BY THE CLOSURE

var counter = 0

let increment = { counter += 1 }

increment()
increment()
increment()
increment()
increment()

counter

func counting() -> (() -> Int) {
    var counter = 0
    let increment: () -> Int = {
        counter += 1
        return counter
    }
    return increment
}

let counter1 = counting()
let counter2 = counting()

counter1()
counter2()
counter1()
counter1()
counter2()

// DESIGNED TO BE LIGHTWEIGHT

// NO NAMING OVERHEAD

// MANY WAYS TO SHORTEN SYNTAX

var sum = { (a: Int, b: Int) -> Int in
    return a + b
}

sum = { (a: Int, b: Int) -> Int in
    a + b
}

sum = { (a, b) in a + b }

sum = { $0 + $1 }

func greet(hello: () -> Void) {
    hello()
}

greet {
    print("hello world")
}

let students: Set = ["Kofi", "Abena", "Peter", "Kweku", "Akosua"]

let sortedStudents = students.sorted()

students.sorted {
  $0.count > $1.count
}

var prices = [1.5, 10, 4.99, 2.30, 8.19]

let largePrices = prices.filter {
    return $0 > 5
}

let salePrices = prices.map {
  return $0 * 0.9
}

let stock = [1.5:5, 10:2, 4.99:20, 2.30:5, 8.19:30]

let stockSum = stock.reduce(0) {
  return $0 + $1.key * Double($1.value)
}

import UIKit

DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
    print("Hello world!")
}


let url = URL(string: "https://www.example.com/")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
    if let data = data {
        let string = String(data: data, encoding: .utf8)!
        print(string)
    }
}
task.resume()