I am new to swift and learning swift from "The Swift Programming Language(Swift 3 beta)". Below is a simple example from their book of protocol extension
protocol ExampleProtocol {
var simpleDescription: String {get}
mutating func adjust()
}
class SimpleClass: ExampleProtocol {
var simpleDescription: String = "A vert simple class."
var anotherProperty: Int = 69105
func adjust() {
simpleDescription += "Now 100% adjusted."
}
}
var a = SimpleClass()
a.adjust()
let aDescripition = a.simpleDescription
struct SimpleStructure: ExampleProtocol {
var simpleDescription: String = "A simple structure"
mutating func adjust() {
simpleDescription += "(adjusted)"
}
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription
extension Int: ExampleProtocol{
var simpleDescription : String {
return "The number \(self)"
}
mutating func adjust() {
self += 42
}
}
//var c = SimpleClass()
//c.adjust()
print(7.simpleDescription)
The end print result is "The number 7\n". As you can see that in extension, we have mutating function that add 42 to self. My question is that how can we call mutating function in extension so that result is added value of +42.
How we call mutating function in extension so that result is added value of +42.?
The function that results in the added value of +42 is the adjust() function of Int. To call it, just run this:
var c = 7
c.adjust()
print(c)
c is 49 (7 + 42)
Related
I have code like this:
class A{}
class B: A{
var val = 1
}
class C: A{
var num = 5
}
extension Optional where Wrapped == [B?]{
var vals: [B]{
var result = [B]()
if let arr = self{
for part in arr{
if let val = part{
result.append(val)
}
}
}
return result
}
}
extension Optional where Wrapped == [C?]{
var vals: [C]{
var result = [C]()
if let arr = self{
for part in arr{
if let val = part{
result.append(val)
}
}
}
return result
}
}
var one: [B?]? = [B()]
var two: [C?]? = [C(), nil]
print(one.vals.count)
print(two.vals.count)
Here is the optimized one:
Combined into one, for B ( A's subclass ) & C ( A's subclass )
extension Optional where Wrapped: Collection{
var vals: [A]{
var result = [A]()
if let arr = self{
for part in arr{
if let val = part as? A{
result.append(val)
}
}
}
return result
}
}
Now question comes,
for case like the follwing,
how to go on the optimization?
print(one.vals.first?.val ?? "")
print(two.vals.first?.num ?? "")
I guess, I need a function to return an object's real type
PS: I know , to handle data , struct is perfect with protocol
While it's a company project, & I'm a new one
You need to introduce an extra type variable to say that the extension works on Optionals where Wrapped.Element is another Optional of any type. You have to express the "any type" part with another type variable, but you cannot add this type variable in the extension's declaration (though this feature is being proposed), or the property's declaration. What you can do instead, is to make vals a function:
func vals<T>() -> [T] where Wrapped.Element == T? {
var result = [T]()
if let arr = self{
for part in arr{
if let val = part{
result.append(val)
}
}
}
return result
}
Note that this can be simplified to:
extension Optional where Wrapped: Sequence {
func vals<T>() -> [T] where Wrapped.Element == T? {
self?.compactMap { $0 } ?? []
}
}
Just for fun. Another possible approach to keep it as a computed property instead of a generic method is to create an AnyOptional protocol with an associatedtype Wrapped and conform Optional to it. Then you can create a computed property to return an array of its Wrapped Element Wrapped type:
protocol AnyOptional {
associatedtype Wrapped
var optional: Optional<Wrapped> { get }
}
extension Optional: AnyOptional {
var optional: Optional<Wrapped> { self }
}
extension AnyOptional where Wrapped: Sequence, Wrapped.Element: AnyOptional {
var elements: [Wrapped.Element.Wrapped] {
optional?.compactMap(\.optional) ?? []
}
}
print(one.elements) // "[B]\n"
print(two.elements) // "[C]\n"
print(one.elements.first?.val ?? "") // "1\n"
print(two.elements.first?.num ?? "") // "5\n"
I have a protocol FooProtocol. and a class Bar<Foo:FooProtocol>. Inside a class an Array var mess: [Foo?]? to keep [foo1, foo2, nil, foo3...] or nil
And I try to make extension for this array to count new Foo object. I prefer to have protocols, because Foos could be very different objects delivered from outer world.
protocol FooProtocol {
....
init(from heaven: Int)
}
extension Optional where
Wrapped: Collection,
Wrapped.Element == Optional,
Wrapped.Element.Wrapped: FooProtocol // 'Wrapped' is not a member type of 'Wrapped.Element'
{
var united: Wrapped.Element.Wrapped { // Nope
let i = ...
return Wrapped.Element.Wrapped(from: i) // Nope
}
}
class Bar<Foo:FooProtocol> {
var mess: [Foo?]?
init (with mess: [Foo?]?) {
self.mess = mess
}
var important: Foo {
return mess.united
}
}
Any ideas? I'm blocked.
Edit 1:
After Leo suggestions I changed some parts of my code. But still stucked. This time more code from Playgrounds.
Any object that could be converted into '[Double]'. Could be color (as RGBA), Bezier curve, square, whatever...
public protocol FooProtocol {
var atomized: () -> [Double] {get}
static var count: Int {get}
init(_ array:[Double])
init()
}
public extension Array where Element: FooProtocol {
var average: Element {
var resultAtoms: [Double] = []
let inputAtoms = self.map {$0.atomized()}
for i in 0..<Element.count {
let s = inputAtoms.reduce(into: 0.0, {$0 += $1[i]}) / Double (Element.count)
resultAtoms.append(s)
}
return Element(resultAtoms)
}
}
extension Optional where
Wrapped: Collection,
Wrapped.Element == Optional<FooProtocol>
{
typealias Foo = Wrapped.Element.Wrapped // Doesn't work. How to get class?
var average: Foo { // I cannot use Wrapped.Element, it's Optional
if let thatsList = self {
let withOptionals = Array(thatsList) // OK, its [Optional<FooProtocol>]
let withoutOptionals = thatsList.compactMap({$0}) // OK, its [FooProtocol]
// This is funny, called from class works and makes 'bingo'.
return withoutOptionals.average // Error: Value of protocol type 'FooProtocol' cannot conform to 'FooProtocol'; only struct/enum/class types can conform to protocols
} else {
return Foo() // Hello? init Wrapped? Foo? How to get Foo()?
}
}
}
class Bar<Foo:FooProtocol> {
var mess: [Foo?]?
init (with mess: [Foo?]?) {
self.mess = mess
}
func workOn() {
let z:Foo = mess.average // OK, I can make 'mess.average ?? Foo()' but prefer not do it
}
// Thats OK
func workHard() { // To prove 'Array extension where Element: FooProtocol' works
if let messExist = mess {
let withoutOptionals = messExist.compactMap({$0})
let bingo = withoutOptionals.average //It's OK
}
}
}
class SomeFoo : FooProtocol {
static var count = 3
required init() {
a = 0
b = 0
c = 0
}
required init(_ array: [Double]) {
self.a = Int(array[0])
self.b = Float(array[1])
self.c = array[2]
}
var atomized: () -> [Double] {
return {return [Double(self.a), Double(self.b), self.c]}
}
var a: Int
var b: Float
var c: Double
}
let aFoo = SomeFoo([1, 2, 3])
let bFoo = SomeFoo([7, 9, 1])
let cFoo = SomeFoo([2, 6, 5])
let barData = [nil, aFoo, nil, bFoo, cFoo]
let barWithData = Bar(with: barData)
let barWithoutData = Bar<SomeFoo>(with: nil)
Maybe I should forget about extending array and make some functions inside a class (I'm almost sure I will need those functions somewhere else)
Edit 2
Even if I try to simplify and to make extension for Array I found troubles.
extension Array where
Element == Optional<FooProtocol>
{
func averageNils <Foo: FooProtocol>() -> Foo {
let withOptionals = Array(self) // OK, its [Optional<FooProtocol>]
let withoutOptionals = self.compactMap({$0}) // OK, its [FooProtocol]
return withoutOptionals.average as! Foo // Error: Value of protocol type 'FooProtocol' cannot conform to 'FooProtocol'; only struct/enum/class types can conform to protocols
}
}
From my understanding, it should work as you did, but one never knows what happens in the swift compiler world (and especially it's error messages).
Anyway, you can circumvent digging deeper into Wrapped.Element.Wrapped by specifyig the Wrapped.Element more precisely to be an Optional<FooProtocol>:
protocol FooProtocol {}
class Foo : FooProtocol {}
extension Optional where
Wrapped: Collection, //OK
Wrapped.Element == Optional<FooProtocol> // still good
{
var unfied: Wrapped.Element // Should be 'Foo' if self is '[Foo?]?' {
{
return 1 == 0 ? nil : Foo()
}
}
I want to "make" a number of class instances similar to a base class but different in underlying type. (Not quite the same as the typical "Animal" class factory examples seen all over the net!)
The code below is close to working but it requires the user to "upcast" the make result, as in:
var f1 = FOO.make(version: FOO.Ver.f1) as! FOO1_32
I do not want the user to know about the specific class type other than it is a FOO. I have seen other proposals and they all indicate that the solution is to define the make with a generic type that conforms to the protocol as in:
make<T: FOOProtocol>(version: Ver = .f1) -> T
However this gives me the error "generic parameter 'T' could not be inferred" on the call to FOO.make(version: FOO.Ver.f1)
Anyone know how to do this? My Playground code follows.
protocol FOOProtocol
{
associatedtype FOOtype
var value: FOOtype {get set}
}
class FOO
{
enum Ver
{
case f1
case f2
}
class func make(version: Ver = .f1) -> FOO
{
print("FOO make")
switch version
{
case .f1:
return FOO1_32()
case .f2:
return FOO2_64()
}
}
}
class FOO1_32: FOO, FOOProtocol
{
typealias FOOtype = UInt32
private var fooVal: UInt32 = 0
var value: UInt32
{
get { return self.fooVal }
set { self.fooVal = newValue }
}
override init()
{
print("FOO1_32 init")
self.fooVal = 132
}
}
class FOO2_64: FOO, FOOProtocol
{
typealias FOOtype = UInt64
private var fooVal: UInt64 = 0
var value: UInt64
{
get { return self.fooVal }
set { self.fooVal = newValue }
}
override init()
{
print("FOO2_64 init")
self.fooVal = 264
}
}
var f1 = FOO.make(version: FOO.Ver.f1) // requires: as! FOO1_32
let f1v = f1.value
print("\(f1v)")
var f2 = FOO.make(version: FOO.Ver.f2) // requires: as! FOO2_64
let f2v = f2.value
print("\(f2v)")
I try to use the set method for calling a function after the value is changed.
I did not see why the set method is not called.
The code could be directly executed in playground
//: Playground - noun: a place where people can play
import UIKit
protocol RandomItem {
var range : (Int,Int) {get set}
var result : Int {get set}
init()
mutating func createRandom()
}
extension RandomItem {
var range : (Int,Int) {
get {
return range
}
set {
range = newValue
self.createRandom()
}
}
}
struct Item: RandomItem {
var range = (0,1)
var result: Int = 0
init() {
self.createRandom()
}
mutating func createRandom() {
let low = UInt32(range.0)
let high = UInt32(range.1)
result = Int(arc4random_uniform(high - low + 1) + low)
}
}
Your struct Item declares its own range property, which overrides the default you created in the protocol extension. The range property in Item has no getters or setters defined to do what your extension version does.
Another issue:
Your protocol extension defines the range property as a computed property (no storage) whose getter and setter both call itself. This will loop infinitely.
Maybe you are looking for something more like:
protocol RandomItem {
var storedRange: (Int, Int) { get }
var range : (Int,Int) {get set}
var result : Int {get set}
init()
mutating func createRandom()
}
extension RandomItem {
var range : (Int,Int) {
get {
return storedRange
}
set {
storedRange = newValue
self.createRandom()
}
}
}
struct Item: RandomItem {
var result: Int = 0
var storedRange = (0, 1)
init() {
self.createRandom()
}
mutating func createRandom() {
let low = UInt32(range.0)
let high = UInt32(range.1)
result = Int(arc4random_uniform(high - low + 1) + low)
}
}
This requires a conforming type to define a stored property storedRange, which the default implementation of the computed property range will interact with.
In Objective-C, one can add a description method to their class to aid in debugging:
#implementation MyClass
- (NSString *)description
{
return [NSString stringWithFormat:#"<%#: %p, foo = %#>", [self class], foo _foo];
}
#end
Then in the debugger, you can do:
po fooClass
<MyClass: 0x12938004, foo = "bar">
What is the equivalent in Swift? Swift's REPL output can be helpful:
1> class MyClass { let foo = 42 }
2>
3> let x = MyClass()
x: MyClass = {
foo = 42
}
But I'd like to override this behavior for printing to the console:
4> println("x = \(x)")
x = C11lldb_expr_07MyClass (has 1 child)
Is there a way to clean up this println output? I've seen the Printable protocol:
/// This protocol should be adopted by types that wish to customize their
/// textual representation. This textual representation is used when objects
/// are written to an `OutputStream`.
protocol Printable {
var description: String { get }
}
I figured this would automatically be "seen" by println but it does not appear to be the case:
1> class MyClass: Printable {
2. let foo = 42
3. var description: String { get { return "MyClass, foo = \(foo)" } }
4. }
5>
6> let x = MyClass()
x: MyClass = {
foo = 42
}
7> println("x = \(x)")
x = C11lldb_expr_07MyClass (has 1 child)
And instead I have to explicitly call description:
8> println("x = \(x.description)")
x = MyClass, foo = 42
Is there a better way?
To implement this on a Swift type you must implement the CustomStringConvertible protocol and then also implement a string property called description.
For example:
class MyClass: CustomStringConvertible {
let foo = 42
var description: String {
return "<\(type(of: self)): foo = \(foo)>"
}
}
print(MyClass()) // prints: <MyClass: foo = 42>
Note: type(of: self) gets the type of the current instances instead of explicitly writing ‘MyClass’.
Example of using CustomStringConvertible and CustomDebugStringConvertible protocols in Swift:
PageContentViewController.swift
import UIKit
class PageContentViewController: UIViewController {
var pageIndex : Int = 0
override var description : String {
return "**** PageContentViewController\npageIndex equals \(pageIndex) ****\n"
}
override var debugDescription : String {
return "---- PageContentViewController\npageIndex equals \(pageIndex) ----\n"
}
...
}
ViewController.swift
import UIKit
class ViewController: UIViewController
{
/*
Called after the controller's view is loaded into memory.
*/
override func viewDidLoad() {
super.viewDidLoad()
let myPageContentViewController = self.storyboard!.instantiateViewControllerWithIdentifier("A") as! PageContentViewController
print(myPageContentViewController)
print(myPageContentViewController.description)
print(myPageContentViewController.debugDescription)
}
...
}
Which print out:
**** PageContentViewController
pageIndex equals 0 ****
**** PageContentViewController
pageIndex equals 0 ****
---- PageContentViewController
pageIndex equals 0 ----
Note: if you have a custom class which does not inherit from any class included in UIKit or Foundation libraries, then make it inherit of NSObject class or make it conform to CustomStringConvertible and CustomDebugStringConvertible protocols.
Just use CustomStringConvertible and var description: String { return "Some string" }
works in Xcode 7.0 beta
class MyClass: CustomStringConvertible {
var string: String?
var description: String {
//return "MyClass \(string)"
return "\(self.dynamicType)"
}
}
var myClass = MyClass() // this line outputs MyClass nil
// and of course
print("\(myClass)")
// Use this newer versions of Xcode
var description: String {
//return "MyClass \(string)"
return "\(type(of: self))"
}
The answers relating to CustomStringConvertible are the way to go. Personally, to keep the class (or struct) definition as clean as possible, I would also separate out the description code into a separate extension:
class foo {
// Just the basic foo class stuff.
var bar = "Humbug!"
}
extension foo: CustomStringConvertible {
var description: String {
return bar
}
}
let xmas = foo()
print(xmas) // Prints "Humbug!"
class SomeBaseClass: CustomStringConvertible {
//private var string: String = "SomeBaseClass"
var description: String {
return "\(self.dynamicType)"
}
// Use this in newer versions of Xcode
var description: String {
return "\(type(of: self))"
}
}
class SomeSubClass: SomeBaseClass {
// If needed one can override description here
}
var mySomeBaseClass = SomeBaseClass()
// Outputs SomeBaseClass
var mySomeSubClass = SomeSubClass()
// Outputs SomeSubClass
var myOtherBaseClass = SomeSubClass()
// Outputs SomeSubClass
As described here, you can also use Swift's reflection capabilities to make your classes generate their own description by using this extension:
extension CustomStringConvertible {
var description : String {
var description: String = "\(type(of: self)){ "
let selfMirror = Mirror(reflecting: self)
for child in selfMirror.children {
if let propertyName = child.label {
description += "\(propertyName): \(child.value), "
}
}
description = String(description.dropLast(2))
description += " }"
return description
}
}
struct WorldPeace: CustomStringConvertible {
let yearStart: Int
let yearStop: Int
var description: String {
return "\(yearStart)-\(yearStop)"
}
}
let wp = WorldPeace(yearStart: 2020, yearStop: 2040)
print("world peace: \(wp)")
// outputs:
// world peace: 2020-2040