Computed properties in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a computed property in Swift?

A computed property does not store a value directly. Instead, it provides a getter and optionally a setter to calculate a value when accessed or set.

beginner

How do you define a read-only computed property in Swift?

You define a computed property with only a getter and no setter. For example:<br>

var area: Double {<br>  return width * height<br>}

intermediate

Can computed properties have side effects in Swift?

Yes, computed properties can run code inside their getter or setter, so they can have side effects like logging or updating other values.

beginner

What is the difference between stored and computed properties?

Stored properties hold actual values in memory. Computed properties calculate values on demand without storing them.

intermediate

Show an example of a computed property with both getter and setter in Swift.

Example:<br>

var temperatureCelsius: Double {<br>  get { return (temperatureFahrenheit - 32) * 5 / 9 }<br>  set { temperatureFahrenheit = newValue * 9 / 5 + 32 }<br>}

What does a computed property in Swift do?

A Cannot have a setter

B Stores a fixed value in memory

C Calculates a value when accessed

D Only stores strings

Computed properties calculate and return a value when accessed, instead of storing it.

Which keyword is used to define a computed property in Swift?

A let

B var

C func

D class

Computed properties are defined using 'var' because their value can change.

Can a computed property have a setter in Swift?

A Yes, to allow setting a new value

B No, computed properties are read-only

C Only if marked with 'let'

D Only inside structs

Computed properties can have a setter to update related values.

What happens if a computed property has only a getter?

A It causes a compile error

B It can be set

C It stores a value

D It is read-only

A computed property with only a getter is read-only.

Which of these is NOT true about computed properties?

A They store values directly

B They can have side effects

C They use get and set blocks

D They calculate values on demand

Computed properties do not store values directly; they calculate them.

Explain what a computed property is and how it differs from a stored property in Swift.

Think about how values are stored or calculated.

Write a simple Swift computed property that calculates the area of a rectangle given width and height stored properties.

Use a getter to calculate the area.