Swift - Optionals - Versionsgeschichte

134.3.86.14 am 6. Januar 2023 um 08:03 Uhr

2023-01-06T08:03:33Z

134.3.86.14: /* Optional Anwendungsfälle */

2023-01-06T07:37:36Z

Optional Anwendungsfälle

134.3.86.14 am 6. Januar 2023 um 07:35 Uhr

2023-01-06T07:35:27Z

134.3.86.14: Die Seite wurde neu angelegt: „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…“

2022-12-28T20:40:11Z

Die Seite wurde neu angelegt: „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…“

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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

<syntaxhighlight lang="swift">
/**
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

</syntaxhighlight>

← Nächstältere Version		Version vom 6. Januar 2023, 08:03 Uhr
Zeile 1:		Zeile 1:
		+	== Links ==
		+	[[Swift (Programmiersprache)]]
		+
		+	== Optionals ==
		+
	Optionals are a way to prevent code from running in a null exeption.		Optionals are a way to prevent code from running in a null exeption.

@@ Zeile 67: / Zeile 67: @@
 let myStruct: MyStruct? // optional caus not initialized yet
 myStruct = MyStruct() // now it is initialised
-print(myStruct?.myProperty ?? "myStuct is nil")
+print(myStruct?.myProperty ?? "myStuct is nil - cannot access myProperty")
 /**
   Used for optional structs or classes I
@@ Zeile 73: / Zeile 73: @@
   optional?.method
   ONLY IF OPTIONAL IS INITIALISED method will execute or property will accessed
   */
 </syntaxhighlight>

← Nächstältere Version		Version vom 6. Januar 2023, 07:35 Uhr
Zeile 16:		Zeile 16:
	print(playerName ?? "no name given") // shorthand for the line above		print(playerName ?? "no name given") // shorthand for the line above

		+	</syntaxhighlight>
		+
		+	== Optional Anwendungsfälle ==
		+	<syntaxhighlight lang="swift">
		+	// 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")
		+	/**
		+	Used for optional structs or classes I
		+	optional?.property
		+	optional?.method
		+	ONLY IF OPTIONAL IS INITIALISED method will execute or property will accessed
		+
		+	*/
	</syntaxhighlight>		</syntaxhighlight>