Swift is Confusing: Classes, Structures, Designated Initializers, Instance Methods, Type Methods, Functions, Methods, Convenience Initializers & External Parameter Names

Swift is Confusing

Class vs Structs

Both: Store values, initialize, subscripts, extensible & protocol

Class can inherit, de-initialize, reference counting & typecast

Functions vs Methods

Methods are FUNCTIONS INSIDE A CLASS

Functions can be inside or OUTSIDE A CLASS!

Cannot use functionName(param1,param2) to call a function declared inside a class {}

Methods:

1. It is implicitly passed the object for which it was called
2. It is able to operate on data that is contained within the class

Instance Methods vs Type Methods (Instance Method vs Class Methods I think)

Methods are functions that are associated with a particular type. Classes, structures, and enumerations can all define instance methods, which encapsulate specific tasks and functionality for working with an instance of a given type. Classes, structures, and enumerations can also define type methods, which are associated with the type itself. Type methods are similar to class methods in Objective-C.

• class Counter {
• var count = 0
• func increment() {
• count++
• }
• }
• let counter = Counter()
• counter.increment()

vs

• class SomeClass {
• class func someTypeMethod() {
• // type method implementation goes here
• }
• }
• SomeClass.someTypeMethod()

Class Factory vs Initializer

This is not particular to Swift but may come up in searches.  A Class Factory method is what was know in ObjC as factory methods and I even saw them references as convenience methods or constructors.  These are instead of:

NSArray *someArray = [[NSArray alloc] init]];

they would be:

NSArray *someArray = [NSArray arrayWithObjects:@”One”, @”Two”];

Another example:

• UITableView *myTableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStyleGrouped];
• let myTableView: UITableView = UITableView(frame: CGRectZero, style: .Grouped)

ObjC class or factory methods get mapped as convenience initializers in Swift.  So:

• UIColor *color = [UIColor colorWithRed:0.5 green:0.0 blue:0.5 alpha:1.0];

gets translated into this:

• let color = UIColor(red: 0.5, green: 0.0, blue: 0.5, alpha: 1.0)

Designated Initializer vs Convenience Initializer

A designated initializer calls its superclass’ init and defines all values added by the self class.  Unless explicitly provided, a class inherits a super initializer from its superclass.

Any other convenience initializer calls self.init and have the convenience keyword before the init keyword.

Initialization must be done in order; own properties, super, super properties.

Initializers & Optionals in one 🙂

• class SurveyQuestion {
• let text: String
• var response: String?
• init(text: String) {
• self.text = text
• }
• func ask() {
• println(text)
• }
• }
• let beetsQuestion = SurveyQuestion(text: "How about beets?")
• beetsQuestion.ask()
• // prints "How about beets?"
• beetsQuestion.response = "I also like beets. (But not with cheese.)"

Default Initializers

• class ShoppingListItem {
• var name: String?
• var quantity = 1
• var purchased = false
• }
• var item = ShoppingListItem()

All non-optional values are supplied with a default value and it is a Base Class (because it doesn’t have a super class)

Diagram:

class A {
    var x: Int
    convenience init() {
        self.init(x: 0)
    }
    init(x: Int) {
        self.x = x
    }
}

where init(x:Int) is the designated initializer and any other must have the convenience keyword.

class B: A {
    var y: Int
    convenience init() {
        self.init(y: 0)
    }
    convenience init(y: Int) {
        self.init(x: 0, y: y)
    }
    init(x: Int, y: Int) {
        self.y = y
        super.init(x: x)
    }
}

Parameter Names / Externals / The first

//Default: First Parameter is the local parameter (don't need to specify it), the rest are external parameters
    func greet (name: String, day: String) -> String {
        return "Hello \(name), today is \(day)."
    }
greet("John", day:"Monday")
    //Use Hash symbol to make the First parameter as external parameter
    func greet2 (#name: String, day: String) -> String {
        return "Hello \(name), today is \(day)."
    }
greet(name:"John", day:"Monday")