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iOS Object-Oriented Swift Classes and Objects Designated Initializer

Posted by Juan Cabral
Juan Cabral
4,318 Points

Why in the init method we can change title if it is a constant? Inside the class its behavior is like a variable?

For example in Java if I declare a constant inside a class it cannot be modified like the example provided below: 

public class Product {

     final String title = "";

    public Product(String title){
        this.title = title; //this is an error

    }

1 Answer

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

assigning a value to a constant property when you declare it sets its default value. if the constant is assigned a value during initialization that default value is ignored, and the value assigned in the init method is used instead.

from the Swift eBook:

You can set the initial value of a stored property from within an initializer, as shown above. Alternatively, specify a default property value as part of the property’s declaration. You specify a default property value by assigning an initial value to the property when it is defined.

Chris Shaw
Chris Shaw
26,676 Points
Chris Shaw
Chris Shaw
26,676 Points

The constructor actually overrules the constant altogether, see the below example which functions perfectly fine in Xcode 6.1.1.

class Product {
    let title: String = "[Unknown]"
    let price: Double = 99.0

    init(title: String, price: Double) {
        self.title = title
        self.price = price
    }
}

let tv = Product(title: "Samsung Smart TV", price: 10000.00)
Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

good catch, edited my initial post. looks like the values assigned at declaration are just default values that only stick if the property is not assigned a value in init