Playground, enum, Optional, cast
Video Description
Playground
Swift has a very cool feature that allows you to write a code and get a quick result at the right side of the screen. In order to make a Playground file you should open the Xcode. From the left hand side of the screen select "Get started with a playground". From the opening window add a name for your file and choose the platform you want to code (for this tutorial select iOS) and then give it a location to save. t opens a blank page that you can write your code there. In order to test the playground, copy paste the code that we wrote in previous tutorial.
enum
There are 3 categories that we can code in Swift (class, struct and enum). One of the categories are called enum. Here is how we define enum in swift:
enum Gender {
case Male
case Female
}
Then we can use it like bellow:
var huxTek: Gender huxTek = Gender.Male
We can alsowrite only .Male like this:
huxTek = .Male
we can have a switch for this enum like bellow:
switch huxTek {
case .Male:
print("A man")
case .Female:
print("A woman")
}
Optional !?
One of the important subjects that you should get familiar early in the game is optional type. You gonna see optional type in many place and actually you will use it a lot during swift programming. That's why I dedicated a separate session just for Optional type.
Optional is just an enum with 2 cases like bellow:
One case is none or null and the other case is something and something could be any type (String, Array, Int, ...). In order to explain it in an example, lets define a dictionary.
The output of the above code is:
The reason that we have the word Optional around the val1 is because myDict["key1"] returns an optional. It means that it could have some value or nil. In order to unwrap the optional you should put ! after the optional value like bellow:
The output of the above code is:
We have learned how to unwrap optional into a type, now we need to know how to define an optional type. It's very easy, you just have to add a question mark after the type of the variable.
enum Optional{
case None
case Some(T)
}
var myDict = [String:String]()
myDict = [
"key1": "val1",
"key2": "val2",
"key3": "val3"
]
print(myDict["key1"])
"Optional("val1")\n"
Unwrap Optional !
print(myDict["key1"]!)
"val1"\n
Optional binding
In order to assign an optional type into a variable safely we should use the following pattern:
if let key1Val = myDict["key1"] {
print(key1Val)
}
Cast
Imagine our dictionary includes key as String and value as String or another dictionary. The way we define it is like bellow. Since we don't know if it's String or a dictionary we just use a type called AnyObject. It means any type.
var myDict = [String:AnyObject]()
myDict = [
"key1": ["subKey1":"subVal1"],
"key2": ["dasda", "asdasd"],
"key3": "val3"
]
If we define a variable to get "key1" value, it returns the type as AnyObject because it doesn't know the type. In order to define a type for it we need to cast it like bellow:
var sub1Key1Value = myDict["key1"] as! [String:String]Now it knows that the type is a dictionary with key as String and value as String. In order to safely check if an object is a certain type we can use "is" function as bellow:
if myDict["key1"] is [String:String] {
var sub1Key1Value = myDict["key1"] as! [String:String]
print(sub1Key1Value["subKey1"]!)
}
?We have learned how to unwrap optional into a type, now we need to know how to define an optional type. It's very easy, you just have to add a question mark after the type of the variable.
var myString: String?It's very important to know that after we put question mark, the variable is no longer a String type. It's type optional that could be String. In order to print it out we need to unwap it with !
