[Swift]: Learning 1

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I have recently started to learn Swift in Xcode--the following swift posts will be coming from a free course provided by Standford University.

Syntax: Argument

@IBAction func touchCard(ExternalArg InternalArg: UIButton) {

}

Swift can have different types of argument.

1. Having one argument: used in both outside and inside the function
2. Having two arguments: external/internal arguments. Former is used outside the function and latter is used inside the function.

Here's an example of usage of external / internal names

@IBAction func touchCard(_ sender: UIButton){
    flipCard(withEmoji: "👻", on: sender)
}
func flipCard(withEmoji emoji: String, on button: UIButton){
    if button.current = emoji {

    }
}

func touchCard uses withEmoji(external name) while func flipCard uses emoji(internal name).

Return value

@IBAction func touchCard(oneArg sender: UIButton) -> int {

}

Swift uses -> to denote the return value of a func

Int?

func firstIndex(of elemment: UIButton) -> Int?

Int? is not an int. This return value is an optional, different type entirely from int. Optional has two states: set or not set.

Optional

let cardNum = cardButtons.firstIndex(of: sender)!

Putting ! at the end assumes that the optional is set. By doing this, it may cause a fatal error when the optional is not set. Thus, it may be a better practice to have if/else block w/o !:

if let cardNum = cardButtons.firstIndex(of: sender){

} else{

}

Creating a model (class)

In Xcode, command + N to create a new file to create a new class.

class Concentration{

}

Whenever creating a class, always think about what the public API(Application Programming Interface) would look like

for loop

init(numPairs: Int){
    // 0..<numPairs: does not include numPairs. Use ... for inclusive
    // Use _ when we don't care about what identifier is
    for _ in 0..<numPairs {
        let card = Card()
    }
}

struct

struct Card {
    var isFaceUp = false
    var isMatched = false
    static var identifierFactory = 0

    init() {
        self.identifier = Card.getUniqueIdentifier()
    }

    static func getUniqueIdentifier() -> Int {
        identifierFactory += 1
        return Card.identifierFactory
    }
}

struct and class are similar but:

• No inheritance in struct
• structs are value types and classes are reference types
  • value type: when gets passed in argument, used in array, or assigned to another variable, it gets copied
    • Note: Array Int String Dictionary are structs; they get constantly get copied
• In contrast, class is a reference type. It lives in heap with pointer to it. When you pass somthing you pass the pointer not the actual thing.