Class declaration syntax in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic syntax to declare a class in Swift?

Use the <code>class</code> keyword followed by the class name and curly braces. Example:<br><pre>class MyClass {
    // properties and methods
}</pre>

beginner

How do you define a property inside a Swift class?

Inside the class braces, declare a variable or constant using <code>var</code> or <code>let</code>. Example:<br><pre>class Person {
    var name: String
}</pre>

intermediate

How do you create an initializer in a Swift class?

Use the <code>init</code> method inside the class to set up initial values. Example:<br><pre>class Person {
    var name: String
    init(name: String) {
        self.name = name
    }
}</pre>

intermediate

What keyword is used to inherit from another class in Swift?

Use a colon <code>:</code> after the class name followed by the parent class name. Example:<br><pre>class Student: Person {
    var grade: Int
}</pre>

beginner

Can Swift classes have methods? How do you declare one?

Yes, methods are functions inside a class. Declare them with <code>func</code>. Example:<br><pre>class Person {
    func greet() {
        print("Hello!")
    }
}</pre>

Which keyword starts a class declaration in Swift?

A class

B struct

C func

D var

The class keyword is used to declare a class in Swift.

How do you indicate that a class inherits from another class?

A Using a colon <code>:</code> after the class name

B Using the <code>extends</code> keyword

C Using the <code>inherits</code> keyword

D Using parentheses <code>()</code> after the class name

In Swift, inheritance is shown by placing a colon : after the class name followed by the parent class.

What is the purpose of the init method in a Swift class?

A To declare a property

B To initialize the class with starting values

C To create a new method

D To inherit from another class

The init method sets up initial values when creating an instance of the class.

Which keyword do you use to define a method inside a Swift class?

A method

B procedure

C def

D func

Swift uses the func keyword to define methods inside classes.

How do you declare a variable property inside a Swift class?

A propertyName: Type

B let propertyName: Type

C var propertyName: Type

D def propertyName: Type

Use var to declare a variable property that can change value.

Explain how to declare a simple class in Swift with one property and an initializer.

Think about how you create a blueprint for an object with starting values.

Describe how inheritance works in Swift class declarations and how to write it in code.

Inheritance means one class gets features from another.

Practice

1. What is the correct way to start declaring a class named Car in Swift?

easy

A. function Car() { }

B. def Car() { }

C. class Car { }

D. struct Car { }

Solution

1. Step 1: Recognize Swift class syntax

   In Swift, classes start with the keyword class followed by the class name and curly braces.

2. Step 2: Match the correct option

   class Car { } uses class Car { }, which is the correct syntax for declaring a class named Car.

3. Final Answer:

   class Car { } -> Option C

4. Quick Check:

   Swift class declaration = class ClassName { } [OK]

Hint: Look for 'class' keyword followed by name and braces [OK]

Common Mistakes:

• Using 'def' or 'function' which are not Swift keywords
• Confusing struct with class
• Missing curly braces

2. Which of the following is the correct syntax to declare a class with an initializer in Swift?

easy

A. class Person { init(name: String) { self.name = name } var name: String }

B. class Person { var name: String; init(name: String) { self.name = name } }

C. class Person { init(name: String) { name = self.name } var name: String }

D. class Person { var name: String init(name: String) { name = name } }

Solution

1. Step 1: Understand property declaration order

   In Swift, properties should be declared before the initializer for clarity and correctness.

2. Step 2: Check initializer syntax

   The initializer must assign the parameter to the property using self.name = name.

3. Final Answer:

   class Person { var name: String; init(name: String) { self.name = name } } -> Option B

4. Quick Check:

   Properties before init, use self.property = parameter [OK]

Hint: Declare properties before init; assign with self.property = parameter [OK]

Common Mistakes:

• Declaring properties after init causing errors
• Assigning parameter to self incorrectly
• Missing semicolon or braces

3. What will be the output of this Swift code?

class Animal {
    var name: String
    init(name: String) {
        self.name = name
    }
    func speak() -> String {
        return "Hello, I am \(name)"
    }
}

let dog = Animal(name: "Buddy")
print(dog.speak())

medium

A. Hello, I am name

B. Error: Missing initializer

C. Hello, I am

D. Hello, I am Buddy

Solution

1. Step 1: Understand class initialization

   The class Animal has a property name initialized via init(name: String). The instance dog is created with name "Buddy".

2. Step 2: Analyze the speak() method output

   The speak() method returns a string with the name property interpolated. So it returns "Hello, I am Buddy".

3. Final Answer:

   Hello, I am Buddy -> Option D

4. Quick Check:

   String interpolation with property = Hello, I am Buddy [OK]

Hint: Check property value passed to init and used in method [OK]

Common Mistakes:

• Confusing property name with string literal
• Forgetting to call speak() method
• Assuming default values without init

4. Identify the error in this Swift class declaration:

class Book {
    var title: String
    init(title: String) {
        title = title
    }
}

medium

A. Property 'title' is not initialized correctly

B. Missing class keyword

C. Initializer has wrong name

D. No error, code is correct

Solution

1. Step 1: Check property assignment in initializer

   The initializer assigns title = title, which assigns the parameter to itself, not to the property.

2. Step 2: Correct assignment syntax

   It should be self.title = title to assign the parameter value to the property.

3. Final Answer:

   Property 'title' is not initialized correctly -> Option A

4. Quick Check:

   Use self.property = parameter to assign [OK]

Hint: Use self.property = parameter to avoid confusion [OK]

Common Mistakes:

• Assigning parameter to itself instead of property
• Forgetting self keyword
• Assuming implicit assignment

5. You want to create a Swift class Rectangle with properties width and height, and a method area() that returns the area. Which of the following is the correct complete class declaration?

hard

A. class Rectangle {
var width: Double
var height: Double
init(width: Double, height: Double) {
self.width = width
self.height = height
}
func area() -> Double {
return width * height
}
}

B. class Rectangle {
var width: Double
var height: Double
func area() -> Double {
return width * height
}
init(width: Double, height: Double) {
width = width
height = height
}
}

C. class Rectangle {
var width: Double
var height: Double
init(width: Double, height: Double) {
width = width
height = height
}
func area() -> Double {
return width * height
}
}

D. class Rectangle {
var width: Double
var height: Double
init(width: Double, height: Double) {
self.width = width
self.height = height
}
func area() {
width * height
}
}

Solution

1. Step 1: Check property initialization

   Properties width and height must be assigned using self.width = width and self.height = height in the initializer.

2. Step 2: Verify method return type and body

   The area() method must return a Double and use return width * height.

3. Final Answer:

   class Rectangle { var width: Double var height: Double init(width: Double, height: Double) { self.width = width self.height = height } func area() -> Double { return width * height } } -> Option A

4. Quick Check:

   Use self.property in init and return in methods [OK]

Hint: Assign properties with self. and return values in methods [OK]

Common Mistakes:

• Assigning parameters to themselves without self.
• Missing return statement in method
• Incorrect method return type