What are get and set in Swift

Question

I m learning Swift and I m reading The Swift Programming Language from Apple  I don t have any Objective-C background  only PHP  JavaScript  and others  but not Objective-C   On page 24-25 I see this code       Class definition stuff     var perimeter  Double       get           return 3 0   sideLength           set           sideLength   newValue   3 0               Class continues     This part is not specified in the book  and I can t get what those are for  What are get and set

User · Answer

variable declares and call like this in a class

class X {
    var x: Int = 3

}
var y = X()
print("value of x is: ", y.x)

//value of x is:  3

now you want to program to make the default value of x more than or equal to 3. Now take the hypothetical case if x is less than 3, your program will fail. so, you want people to either put 3 or more than 3. Swift got it easy for you and it is important to understand this bit-advance way of dating the variable value because they will extensively use in iOS development. Now let's see how get and set will be used here.

class X {
    var _x: Int = 3
    var x: Int {
        get {
            return _x
        }
        set(newVal) {  //set always take 1 argument
            if newVal >= 3 {
             _x = newVal //updating _x with the input value by the user
            print("new value is: ", _x)
            }
            else {
                print("error must be greater than 3")
            }
        }
    }
}
let y = X()
y.x = 1
print(y.x) //error must be greater than 3
y.x = 8 // //new value is: 8

if you still have doubts, just remember, the use of get and set is to update any variable the way we want it to be updated. get and set will give you better control to rule your logic. Powerful tool hence not easily understandable.

User · Answer

The getting and setting of variables within classes refers to either retrieving   getting   or altering   setting   their contents   Consider a variable members of a class family  Naturally  this variable would need to be an integer  since a family can never consist of two point something people   So you would probably go ahead by defining the members variable like this   class family      var members Int     This  however  will give people using this class the possibility to set the number of family members to something like 0 or 1  And since there is no such thing as a family of 1 or 0  this is quite unfortunate   This is where the getters and setters come in  This way you can decide for yourself how variables can be altered and what values they can receive  as well as deciding what content they return   Returning to our family class  let s make sure nobody can set the members value to anything less than 2   class family     var  members Int   2   var members Int      get        return  members         set  newVal         if newVal  gt   2           members   newVal        else          println  error  cannot have family with less than 2 members                       Now we can access the members variable as before  by typing instanceOfFamily members  and thanks to the setter function  we can also set it s value as before  by typing  for example  instanceOfFamily members   3  What has changed  however  is the fact that we cannot set this variable to anything smaller than 2 anymore   Note the introduction of the  members variable  which is the actual variable to store the value that we set through the members setter function  The original members has now become a computed property  meaning that it only acts as an interface to deal with our actual variable

User · Answer

A simple question should be followed by a short  simple and clear answer    When we are getting a value of the property it fires its get   part  When we are setting a value to the property it fires its set   part    PS  When setting a value to the property  SWIFT automatically creates a constant named  newValue    a value we are setting  After a constant  newValue  becomes accessible in the property s set   part   Example   var A Int   0 var B Int   0  var C Int   get  return 1  set  print  Recived new value   newValue    and stored into  B          B   newValue             When we are getting a value of C it fires get   part of C property A   C  A              Now A   1    When we are setting a value to C it fires set   part of C property C   2 B              Now B   2

User · Answer

You should look at Computed Properties  In your code sample  perimeter is a property not backed up by a class variable  instead its value is computed using the get method and stored via the set method - usually referred to as getter and setter   When you use that property like this   var cp   myClass perimeter   you are invoking the code contained in the get code block  and when you use it like this   myClass perimeter   5 0   you are invoking the code contained in the set code block  where newValue is automatically filled with the value provided at the right of the assignment operator   Computed properties can be readwrite if both a getter and a setter are specified  or readonly if the getter only is specified

[swift] What are 'get' and 'set' in Swift?

Examples related to swift

Examples related to accessor