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iOS Intermediate Swift 2 Value Semantics, Type Methods and Inheritance Mixed Semantics

Posted by Paul Jackson
Paul Jackson
7,585 Points

Mixed Semantics - value types mixed with reference types can change

In the example presented in the video:

import UIKit

struct Shape {
    let shapeView: UIView

    init(width: CGFloat, height: CGFloat, color: UIColor) {
        let frame = CGRect(x: 0, y: 0, width: width, height: height)

        shapeView = UIView(frame: frame)

        shapeView.backgroundColor = color
    }
}

let square = Shape(width: 100, height: 100, color: .redColor())
square.shapeView.backgroundColor = .blueColor()

Is it accurate to say that the color of the square is allowed to be modified because UIView is class and therefore a reference type? And since the shapeView defined as a constant is it means that the values can be changed, but you could not the reference to what shapeView is pointing to in memory?

3 Answers

Tassia Castro
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.a{fill-rule:evenodd;}techdegree
Tassia Castro
iOS Development Techdegree Student 9,170 Points
Tassia Castro
.a{fill-rule:evenodd;}techdegree
Tassia Castro
iOS Development Techdegree Student 9,170 Points

Is it accurate to say that the color of the square is allowed to be modified because UIView is class and therefore a reference type?

You are totally right. If UiView were a Struct, that means a value type, you wouldn’t be able to change the backgroundColor.

And since the shapeView defined as a constant is it means that the values can be changed, but you could not the reference to what shapeView is pointing to in memory?

Exactly. You are right. As shapeView was declared as a constant, you can only assign a UiView once. But ‘the values’ (backgroundColor) can be changed because UIView is a class and backgroundColor is a Var property inside UIView.

Paul Jackson
Paul Jackson
7,585 Points

Sweet! Thank you!

Boris Likhobabin
Boris Likhobabin
3,581 Points
Boris Likhobabin
Boris Likhobabin
3,581 Points

A liitle off the topic but could you please explain why there is no SELF. in front of shapeView in initializer. Aren't we supposed to do that?

Tassia Castro
seal-mask
.a{fill-rule:evenodd;}techdegree
Tassia Castro
iOS Development Techdegree Student 9,170 Points
Tassia Castro
.a{fill-rule:evenodd;}techdegree
Tassia Castro
iOS Development Techdegree Student 9,170 Points

Hey Boris,

You use self in front of a property during initialisation when the parameter of init() has the same name as the property of the class.

Check this simple example:

class car {

    var name: String
    var color: String

    init(name: String, color: String) {
        self.name = name
        self.color = color
    }
}

In this example if you don't use self the compiler will get confused. It will not know which one is the self property or the parameter received through the init().

So, going back to your question, as the init() does not have any parameter called shapeView, you don't need to use self and the compiler knows you mean self.shapeView.