Swift Property Observers

This is an exit ticket on Swift Property Observers. I copied this material from the Apple site that gives the details of subjects in Swift coding. Here is a link to the document I created for presentation to my students and then to have them complete this exit ticket. I always allow my students to have access to this document as they complete this exit ticket. Here is the link: https://docs.google.com/document/d/1BJ6DaYocUzVsvmJBm7WDWZi5jwCRRPdb/edit?usp=sharing&ouid=102362467938526371992&rtpof=true&sd=true

• I get it.

• I don't get it.

What is the purpose of property observers?

• a) To calculate the value of a property

• b) To monitor changes to a property’s value and respond with custom actions

• c) To initialize stored properties during instance creation

• d) To enable lazy initialization of properties

Answer explanation

Correct Answer: b
Explanation: Property observers allow you to execute custom code whenever a property’s value changes.

What is the primary difference between stored properties and computed properties?

• a) Stored properties calculate their value, while computed properties store it.

• b) Stored properties store a value, while computed properties calculate it.

• c) Both stored and computed properties are only provided by classes.

• d) Stored properties and computed properties are always constant.

Answer explanation

Correct Answer: b
Explanation: Stored properties save a constant or variable value, while computed properties dynamically calculate their value using a getter and (optionally) a setter.

Which of the following can define stored properties?

• a) Classes only

• • b) Classes and structures only

• c) Classes, structures, and enumerations

• d) Enumerations only

Answer explanation

Correct Answer: b
Explanation: Stored properties can be defined by classes and structures, but not by enumerations.

On which types of properties can property observers be added?

• A. Only stored properties defined by the user.

• B. Only computed properties.

• C. Both stored and computed properties.

• D. Only inherited properties in a subclass.

Answer explanation

Correct Answer: A
Explanation: Property observers can be added to stored properties defined by the user or inherited from a superclass.

When are property observers called?

• A. Only when a new value is different from the current value.

• B. Every time a property’s value is set, even if the new value is the same.

• C. Only when a property is initialized.

• D. Only for computed properties.

Answer explanation

• Correct Answer: B
  Explanation: Property observers are triggered every time the property’s value is set, regardless of whether the value is new or the same.

Which types of properties can have property observers?

• A. Only computed properties.

• B. Only stored properties that you define.

• C. Stored properties you define, stored properties you inherit, and computed properties you inherit.

• D. Only inherited properties.

Answer explanation

Correct Answer: C
Explanation: Observers can be added to stored properties (both defined and inherited) and computed properties inherited from a superclass.

How do you add a property observer to an inherited property?

• A. By defining a getter and setter for the property.

• B. By marking the property with @ObservedObject.

• C. By overriding the property in a subclass.

• D. By using a property wrapper.

Answer explanation

Correct Answer: C
Explanation: To add an observer to an inherited property, you override the property in a subclass.

What does the willSet property observer do?

• A. It is called immediately after a value is stored.

• B. It prevents a property’s value from being changed.

• C. It is called just before a new value is stored.

• D. It validates the new value before storage.

Answer explanation

• Correct Answer: C
  Explanation: The willSet observer is called just before the new value is stored.

What is the default parameter name for the new value in a willSet observer?

• A. oldValue

• B. newValue

• C. defaultValue

• D. newParameter

Answer explanation

Correct Answer: B
Explanation: If no custom parameter name is provided, willSet uses the default name newValue.