This is a collection of Swift's convenience extensions I always use. Protocols and operators are also included.

All of the extensions are in the following repository.
https://github.com/tattn/SwiftExtensions

The version of Swift is 4.0.
This is a translated version of the article I wrote in Japanese here.

Get a class name

public protocol ClassNameProtocol {
    static var className: String { get }
    var className: String { get }
}

public extension ClassNameProtocol {
    public static var className: String {
        return String(describing: self)
    }

    public var className: String {
        return type(of: self).className
    }
}

extension NSObject: ClassNameProtocol {}

UIView.className   //=> "UIView"
UILabel().className //=> "UILabel"

Register / Dequeue XIB

UITableView

public extension UITableView {
    public func register<T: UITableViewCell>(cellType: T.Type, bundle: Bundle? = nil) {
        let className = cellType.className
        let nib = UINib(nibName: className, bundle: bundle)
        register(nib, forCellReuseIdentifier: className)
    }

    public func register<T: UITableViewCell>(cellTypes: [T.Type], bundle: Bundle? = nil) {
        cellTypes.forEach { register(cellType: $0, bundle: bundle) }
    }

    public func dequeueReusableCell<T: UITableViewCell>(with type: T.Type, for indexPath: IndexPath) -> T {
        return self.dequeueReusableCell(withIdentifier: type.className, for: indexPath) as! T
    }
}

tableView.register(cellType: MyCell.self)
tableView.register(cellTypes: [MyCell1.self, MyCell2.self])

let cell = tableView.dequeueReusableCell(with: MyCell.self, for: indexPath)

UICollectionView

public extension UICollectionView {
    public func register<T: UICollectionViewCell>(cellType: T.Type, bundle: Bundle? = nil) {
        let className = cellType.className
        let nib = UINib(nibName: className, bundle: bundle)
        register(nib, forCellWithReuseIdentifier: className)
    }

    public func register<T: UICollectionViewCell>(cellTypes: [T.Type], bundle: Bundle? = nil) {
        cellTypes.forEach { register(cellType: $0, bundle: bundle) }
    }

    public func register<T: UICollectionReusableView>(reusableViewType: T.Type,
                                                      ofKind kind: String = UICollectionElementKindSectionHeader,
                                                      bundle: Bundle? = nil) {
        let className = reusableViewType.className
        let nib = UINib(nibName: className, bundle: bundle)
        register(nib, forSupplementaryViewOfKind: kind, withReuseIdentifier: className)
    }

    public func register<T: UICollectionReusableView>(reusableViewTypes: [T.Type],
                                                      ofKind kind: String = UICollectionElementKindSectionHeader,
                                                      bundle: Bundle? = nil) {
        reusableViewTypes.forEach { register(reusableViewType: $0, ofKind: kind, bundle: bundle) }
    }

    public func dequeueReusableCell<T: UICollectionViewCell>(with type: T.Type,
                                                             for indexPath: IndexPath) -> T {
        return dequeueReusableCell(withReuseIdentifier: type.className, for: indexPath) as! T
    }

    public func dequeueReusableView<T: UICollectionReusableView>(with type: T.Type,
                                                                 for indexPath: IndexPath,
                                                                 ofKind kind: String = UICollectionElementKindSectionHeader) -> T {
        return dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: type.className, for: indexPath) as! T
    }
}

collectionView.register(cellType: MyCell.self)
collectionView.register(cellTypes: [MyCell1.self, MyCell2.self])
let cell = collectionView.dequeueReusableCell(with: MyCell.self, for: indexPath)

collectionView.register(reusableViewType: MyReusableView.self)
collectionView.register(reusableViewTypes: [MyReusableView1.self, MyReusableView2.self])
let view = collectionView.dequeueReusableView(with: MyReusableView.self, for: indexPath)

Instantiate a viewController in a storyboard

public enum StoryboardInstantiateType {
    case initial
    case identifier(String)
}

public protocol StoryboardInstantiatable {
    static var storyboardName: String { get }
    static var storyboardBundle: Bundle { get }
    static var instantiateType: StoryboardInstantiateType { get }
}

public extension StoryboardInstantiatable where Self: NSObject {
    public static var storyboardName: String {
        return className
    }

    public static var storyboardBundle: Bundle {
        return Bundle(for: self)
    }

    private static var storyboard: UIStoryboard {
        return UIStoryboard(name: storyboardName, bundle: storyboardBundle)
    }

    public static var instantiateType: StoryboardInstantiateType {
        return .identifier(className)
    }
}

public extension StoryboardInstantiatable where Self: UIViewController {
    public static func instantiate() -> Self {
        switch instantiateType {
        case .initial:
            return storyboard.instantiateInitialViewController() as! Self
        case .identifier(let identifier):
            return storyboard.instantiateViewController(withIdentifier: identifier) as! Self
        }
    }
}

// Class name and Storyboard name, same as Storyboard ID
final class ViewController: UIViewController, StoryboardInstantiatable {
}

ViewController.instantiate()

// Initial view controller & class name and Storyboard name are the same
final class InitialViewController: UIViewController, StoryboardInstantiatable {
    static var instantiateType: StoryboardInstantiateType {
        return .initial
    }
}

InitialViewController.instantiate()

Instantiate a view in XIB

public protocol NibInstantiatable {
    static var nibName: String { get }
    static var nibBundle: Bundle { get }
    static var nibOwner: Any? { get }
    static var nibOptions: [AnyHashable: Any]? { get }
    static var instantiateIndex: Int { get }
}

public extension NibInstantiatable where Self: NSObject {
    public static var nibName: String { return className }
    public static var nibBundle: Bundle { return Bundle(for: self) }
    public static var nibOwner: Any? { return self }
    public static var nibOptions: [AnyHashable: Any]? { return nil }
    public static var instantiateIndex: Int { return 0 }
}

public extension NibInstantiatable where Self: UIView {
    public static func instantiate() -> Self {
        let nib = UINib(nibName: nibName, bundle: nibBundle)
        return nib.instantiate(withOwner: nibOwner, options: nibOptions)[instantiateIndex] as! Self
    }
}

// XIB name and class name are the same & 0th View
final class View: UIView, NibInstantiatable {
}

View.instantiate()

// XIB name and class name are different & & 2nd View
final class View2: UIView, NibInstantiatable {
    static var nibName: String { return "Foo" } // Foo.xib
    static var instantiateIndex: Int { return 2 }
}

View2.instantiate()

Put a custom view created by Xib in Interface Builder

public protocol EmbeddedNibInstantiatable {
    associatedtype Embedded: NibInstantiatable
}

public extension EmbeddedNibInstantiatable where Self: UIView, Embedded: UIView {
    public var embedded: Embedded { return subviews[0] as! Embedded }

    public func configureEmbededView() {
        let view = Embedded.instantiate()
        insertSubview(view, at: 0)
        view.fillSuperview() // described later
    }
}

final class EmbeddedView: UIView, NibInstantiatable {
}

@IBDesignable
final class IBEmbeddedView: UIView, EmbeddedNibInstantiatable {
    typealias Embedded = EmbeddedView

    #if TARGET_INTERFACE_BUILDER
    override func prepareForInterfaceBuilder() {
        super.prepareForInterfaceBuilder()
        configureEmbededView()
    }
    #endif

    override func awakeFromNib() {
        super.awakeFromNib()
        configureEmbededView()
    }
}

Make a view the same size as the superview

public extension UIView {
    public func fillSuperview() {
        guard let superview = self.superview else { return }
        translatesAutoresizingMaskIntoConstraints = superview.translatesAutoresizingMaskIntoConstraints
        if translatesAutoresizingMaskIntoConstraints {
            autoresizingMask = [.flexibleWidth, .flexibleHeight]
            frame = superview.bounds
        } else {
            topAnchor.constraint(equalTo: superview.topAnchor).isActive = true
            bottomAnchor.constraint(equalTo: superview.bottomAnchor).isActive = true
            leftAnchor.constraint(equalTo: superview.leftAnchor).isActive = true
            rightAnchor.constraint(equalTo: superview.rightAnchor).isActive = true
        }
    }
}

superView.addSubview(view)
view.fillSuperview()

Get the top most UIViewController / UINavigationController

public extension UIApplication {
    public var topViewController: UIViewController? {
        guard var topViewController = UIApplication.shared.keyWindow?.rootViewController else { return nil }

        while let presentedViewController = topViewController.presentedViewController {
            topViewController = presentedViewController
        }
        return topViewController
    }

    public var topNavigationController: UINavigationController? {
        return topViewController as? UINavigationController
    }
}

UIApplication.shared.topViewController

Get a view controller which has the view

public extension UIView {
    public var viewController: UIViewController? {
        var parent: UIResponder? = self
        while parent != nil {
            parent = parent?.next
            if let viewController = parent as? UIViewController {
                return viewController
            }
        }
        return nil
    }
}

view.viewController

Create a UIColor by hexadecimal

public extension UIColor {
    public convenience init(hex: Int, alpha: CGFloat = 1.0) {
        let r = CGFloat((hex & 0xFF0000) >> 16) / 255.0
        let g = CGFloat((hex & 0x00FF00) >> 8) / 255.0
        let b = CGFloat(hex & 0x0000FF) / 255.0
        self.init(red: r, green: g, blue: b, alpha: alpha)
    }
}

let color = UIColor(hex: 0xAABBCC)

Remove elements by the instances in an array

public extension Array where Element: Equatable {
    @discardableResult
    public mutating func remove(element: Element) -> Index? {
        guard let index = index(of: element) else { return nil }
        remove(at: index)
        return index
    }

    @discardableResult
    public mutating func remove(elements: [Element]) -> [Index] {
        return elements.flatMap { remove(element: $0) }
    }
}

let array = ["foo", "bar"]
array.remove(element: "foo")
array //=> ["bar"]

Remove the same value from the array

public extension Array where Element: Hashable {
    public mutating func unify() {
        self = unified()
    }
}

public extension Collection where Element: Hashable {
    public func unified() -> [Element] {
        return Array(Set(self))
    }
}

let array = [1, 2, 3, 3, 2, 1, 4]
array.unify() // [1, 2, 3, 4]

Get an element in safety.

public extension Collection {
    public subscript(safe index: Index) -> Element? {
        return startIndex <= index && index < endIndex ? self[index] : nil
    }
}

let array = [0, 1, 2]
if let item = array[safe: 5] {
    print("unreachable")
}

Get substrings with various ranges

public extension String {
    subscript (bounds: CountableClosedRange<Int>) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[start...end])
    }

    subscript (bounds: CountableRange<Int>) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[start..<end])
    }

    subscript (bounds: PartialRangeUpTo<Int>) -> String {
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[startIndex..<end])
    }

    subscript (bounds: PartialRangeThrough<Int>) -> String {
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[startIndex...end])
    }

    subscript (bounds: CountablePartialRangeFrom<Int>) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        return String(self[start..<endIndex])
    }
}

let string = "0123456789"
string[0...5] //=> "012345"
string[1...3] //=> "123"
string[3..<7] //=> "3456"
string[...4]  //=> "01234
string[..<4]  //=> "0123"
string[4...]  //=> "456789"

Create URL from a string / Create URL from a string literal

public extension String {
    public var url: URL? {
        return URL(string: self)
    }
}

extension URL: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        guard let url = URL(string: value) else {
            fatalError("\(value) is an invalid url")
        }
        self = url
    }

    public init(extendedGraphemeClusterLiteral value: String) {
        self.init(stringLiteral: value)
    }

    public init(unicodeScalarLiteral value: String) {
        self.init(stringLiteral: value)
    }
}

if let url = "https://example.com".url {
}

let url: URL = "https://example.com"

Use Kotlin-like scope function

public protocol Appliable {}

public extension Appliable {
    @discardableResult
    public func apply(closure: (Self) -> Void) -> Self {
        closure(self)
        return self
    }
}

public protocol Runnable {}

public extension Runnable {
    @discardableResult
    public func run<T>(closure: (Self) -> T) -> T {
        return closure(self)
    }
}

extension NSObject: Appliable {}
extension NSObject: Runnable {}

let view = UIView().apply {
    $0.backgroundColor = .red
    $0.frame = .init(x: 0, y: 0, width: 200, height: 200)
}

Throw an error by `???` if the value is nil

infix operator ???

public func ???<T>(lhs: T?,
                   error: @autoclosure () -> Error) throws -> T {
    guard let value = lhs else { throw error() }
    return value
}

let value: String? = nil

struct OptionalError: Error {}

do {
    let v = try value ??? OptionalError()
    print(v) // unreachable
} catch {
    print(error) //=> OptionalError
}

Throw an error if there is no key when getting the value from a dictionary

public struct DictionaryTryValueError: Error {
    public init() {}
}

public extension Dictionary {
    func tryValue(forKey key: Key, error: Error = DictionaryTryValueError()) throws -> Value {
        guard let value = self[key] else { throw error }
        return value
    }
}

var dictionary: [String: Int] = [:]
do {
    let value = try dictionary.tryValue(forKey: "foo")
    print(value) // unreachable
} catch {
    print(error) //=> DictionaryTryValueError
}

Create properties and methods accessible with `.ex`

public struct TargetedExtension<Base> {
    let base: Base
    init (_ base: Base) {
        self.base = base
    }
}

public protocol TargetedExtensionCompatible {
    associatedtype Compatible
    static var ex: TargetedExtension<Compatible>.Type { get }
    var ex: TargetedExtension<Compatible> { get }
}

public extension TargetedExtensionCompatible {
    public static var ex: TargetedExtension<Self>.Type {
        return TargetedExtension<Self>.self
    }

    public var ex: TargetedExtension<Self> {
        return TargetedExtension(self)
    }
}

extension UIView: TargetedExtensionCompatible {}

private extension TargetedExtension where Base: UIView {
    func foo() {}
}

UIView().ex.foo()

Blog

My favorite ❤️ Swift extensions

Tatsuya Tanaka

Get a class name

Register / Dequeue XIB

UITableView

UICollectionView

Instantiate a viewController in a storyboard

Instantiate a view in XIB

Put a custom view created by Xib in Interface Builder

Make a view the same size as the superview

Get the top most UIViewController / UINavigationController

Get a view controller which has the view

Create a UIColor by hexadecimal

Remove elements by the instances in an array

Remove the same value from the array

Get an element in safety.

Get substrings with various ranges

Create URL from a string / Create URL from a string literal

Use Kotlin-like scope function

Throw an error by `???` if the value is nil

Throw an error if there is no key when getting the value from a dictionary

Create properties and methods accessible with `.ex`

Join Our Newsletter. No Spam, Only the good stuff.

Related

My favorite ❤️ Swift extensions

Tatsuya Tanaka

Get a class name

Register / Dequeue XIB

UITableView

UICollectionView

Instantiate a viewController in a storyboard

Instantiate a view in XIB

Put a custom view created by Xib in Interface Builder

Make a view the same size as the superview

Get the top most UIViewController / UINavigationController

Get a view controller which has the view

Create a UIColor by hexadecimal

Remove elements by the instances in an array

Remove the same value from the array

Get an element in safety.

Get substrings with various ranges

Create URL from a string / Create URL from a string literal

Use Kotlin-like scope function

Throw an error by ??? if the value is nil

Throw an error if there is no key when getting the value from a dictionary

Create properties and methods accessible with .ex

Join Our Newsletter. No Spam, Only the good stuff.

Related

Throw an error by `???` if the value is nil

Create properties and methods accessible with `.ex`