Swift Closures

closures.swift

import UIKit

struct Student {
    var name: String
    var testScore: Int
}

let students = [
    Student(name: "Ted", testScore: 84),
    Student(name: "Todd", testScore: 79),
    Student(name: "Tom", testScore: 93),
    Student(name: "Terry", testScore: 71)
]

// closure syntax
var topStudentFilter: (Student) -> Bool = { student in
    return student.testScore > 80
}

func topStudentFilterFunc(student: Student) -> Bool {
    return student.testScore > 80
}

// hitting enter on a closure gives you 'trailing closure syntax' (much cleaner)
let topStudents2 = students.filter { student in // type is inferred from array
    return student.testScore > 80
}

let topStudents3 = students.filter {
    $0.testScore > 80 // no return needed b/c it's a one-liner
}

print("top students (closure): \(students.filter(topStudentFilter).count)")
print("top students (func): \(students.filter(topStudentFilterFunc).count)")
print("top students (trailing closure): \(topStudents2.count)")
print("top students (Shorthand syntax for params): \(topStudents3.count)")

// The above all do the same thing, but closures allow you to reuse that bit of code wherever you need it (like an extension or a helper)