Swift - Optionals

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Swift (Programmiersprache)

Optionals

Optionals are a way to prevent code from running in a null exeption.

? declares a optional ! forces a optional to unwrap to original type (with the danger to create an error) ?? is used to give a alternative return if the optional contains nil

/**
 Optionals can provide a kind of safety check if variables not set
 */
//var playerName: String = nil // not working - needs to be a String
var playerName: String? = nil // ? declares Optional so the value can be nil or a string

playerName = "jacktheripper" // try commenting out

print(playerName!) // ! is the counterpart of ? it forces to unwrap to a string - error when playerName not set so it's not good style
if playerName != nil {print(playerName)}else{print("no name given")}
print(playerName ?? "no name given") // shorthand for the line above

Optional Anwendungsfälle

// 5 WAYS TO WORK WITH OPTIONALS
let myOptional: String?
myOptional = "Stephan"

// 1. FORCE UNWRAP
let text:String = myOptional!
/**
 The least safe way  - will crash on runtime if myOptional is nil
 so it totally depends on the user to make sure myOptional is valid.
 */

// 2. Check for nil value
if myOptional != nil{
    print(myOptional!)
}else{
    print("myOptional was found to be nil")
}
/**
 More safe but not comfortable
 */

// 3. OPTIONAL BINDING
if let safeOptional = myOptional {
    print(safeOptional)
}else{
    print("myOptional was found to be nil")
}
/**
 Create a safe version of a optional which we can use safely
 */

// 4. NIL COALESCING OPERATOR
let string: String = myOptional ?? "This is a default value"
/**
 gives us the possibility to provide an alternative value which is used if Optional as nil
 */

// 5. OPTIONAL CHAINING
struct MyStruct {
    var myProperty = 123
    func myMethod(){
        print("I'm a method")
    }
}

let myStruct: MyStruct? // optional caus not initialized yet
myStruct = MyStruct() // now it is initialised
print(myStruct?.myProperty ?? "myStuct is nil - cannot access myProperty")
/**
 Used for optional structs or classes I
 optional?.property
 optional?.method
 ONLY IF OPTIONAL IS INITIALISED method will execute or property will accessed

the compiler checks if myStruct has a value and only if it has than it will go to the chained method 
 
 */