Enum methods and computed properties in Swift - Time & Space Complexity

Time Complexity: Enum methods and computed properties

O(1)

Understanding Time Complexity

We want to understand how the time it takes to run enum methods and computed properties changes as the enum grows.

How does the number of enum cases affect the work done inside its methods or computed properties?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

    enum Direction {
      case north, south, east, west

      func opposite() -> Direction {
        switch self {
        case .north: return .south
        case .south: return .north
        case .east:  return .west
        case .west:  return .east
        }
      }

      var isVertical: Bool {
        self == .north || self == .south
      }
    }
    

This enum has methods and computed properties that return values based on the current case.

Identify Repeating Operations

Look for loops or repeated checks inside the methods or properties.

• Primary operation: The switch statement or equality checks dispatch to the matching case efficiently.
• How many times: Constant time (O(1)) per method call or property access, regardless of case count.

How Execution Grows With Input

The work done does not grow with the number of cases. Swift optimizes enum switches using jump tables or direct dispatch for constant-time execution.

Input Size (number of enum cases)	Approx. Operations
4	1 dispatch
10	1 dispatch
100	1 dispatch

Pattern observation: Operations remain constant independent of the number of enum cases.

Final Time Complexity

Time Complexity: O(1)

This means the execution time is constant, even as the number of enum cases increases.

Common Mistake

[X] Wrong: "Switch statements on enums check cases linearly, so O(n) where n is case count."

[OK] Correct: Swift compiler optimizes exhaustive switches on enums to constant-time dispatch (e.g., jump tables), not linear search.

Interview Connect

Knowing enum methods and properties run in O(1) time demonstrates understanding of compiler optimizations and performance characteristics of Swift data structures.

Self-Check

"What if we replaced the switch with a dictionary lookup? How would the time complexity change? (Hint: Still O(1) average case, but with overhead.)"

Practice

1. What is the purpose of adding methods to an enum in Swift?

easy

A. To inherit properties from other enums

B. To store additional data inside enum cases

C. To perform actions or calculations related to enum cases

D. To convert enums into classes automatically

Solution

1. Step 1: Understand enum methods

   Enum methods allow you to add functions that perform tasks related to the enum's cases.

2. Step 2: Differentiate from other enum features

   Enums do not store extra data like classes; methods help organize related actions.

3. Final Answer:

   To perform actions or calculations related to enum cases -> Option C

4. Quick Check:

   Enum methods = perform actions [OK]

Hint: Methods in enums perform actions tied to cases [OK]

Common Mistakes:

• Thinking enums can inherit from other enums
• Confusing methods with stored properties
• Assuming enums convert to classes automatically

2. Which of the following is the correct syntax to declare a computed property inside an enum in Swift?

easy

A. static var description: String = "Example"

B. func description() -> String { return "Example" }

C. let description = "Example"

D. var description: String { return "Example" }

Solution

1. Step 1: Identify computed property syntax

   Computed properties use var with a code block returning a value, like var name: Type { ... }.

2. Step 2: Check options

   var description: String { return "Example" } matches computed property syntax; B is a method, C is a stored property, D is a static stored property.

3. Final Answer:

   var description: String { return "Example" } -> Option D

4. Quick Check:

   Computed property syntax = var with braces [OK]

Hint: Computed properties use var with braces returning a value [OK]

Common Mistakes:

• Using func instead of var for computed properties
• Declaring computed properties as let constants
• Confusing static stored properties with computed ones

3. Consider this Swift enum with a computed property and method:

enum Direction {
    case north, south, east, west

    var isVertical: Bool {
        return self == .north || self == .south
    }

    func description() -> String {
        switch self {
        case .north: return "Up"
        case .south: return "Down"
        case .east: return "Right"
        case .west: return "Left"
        }
    }
}

let dir = Direction.east
print(dir.isVertical)
print(dir.description())

What is the output?

medium

A. false
Right

B. true
Right

C. false
East

D. true
East

Solution

1. Step 1: Evaluate computed property isVertical

   For Direction.east, isVertical checks if east == north or south, which is false.

2. Step 2: Evaluate description() method

   Switch on east returns "Right" string.

3. Final Answer:

   false Right -> Option A

4. Quick Check:

   east isVertical = false, description = Right [OK]

Hint: Check enum case matches in computed property and switch [OK]

Common Mistakes:

• Assuming east is vertical
• Confusing method return values with case names
• Forgetting to call method with parentheses

4. This Swift enum code has an error:

enum Status {
    case success, failure

    var message: String {
        switch self {
        case .success:
            return "Success"
        case .failure
            return "Failure"
        }
    }
}

What is the error and how to fix it?

medium

A. Computed property must be a function; change to func message() -> String

B. Missing colon after case .failure; add ':' after .failure

C. Enum cases must have raw values; add raw values to cases

D. Return statements are not allowed in computed properties; remove returns

Solution

1. Step 1: Identify syntax error in switch cases

   Case .failure is missing a colon ':' after it, causing a syntax error.

2. Step 2: Fix the syntax

   Add ':' after case .failure to correct the switch syntax.

3. Final Answer:

   Missing colon after case .failure; add ':' after .failure -> Option B

4. Quick Check:

   Switch case syntax requires ':' [OK]

Hint: Switch cases must end with a colon ':' [OK]

Common Mistakes:

• Thinking computed properties need func keyword
• Adding raw values unnecessarily
• Removing return statements inside computed properties

5. You want to create an enum Light with cases red, yellow, and green. Add a computed property time that returns the duration in seconds for each light: red = 30, yellow = 5, green = 25. Also add a method next() that returns the next light in the traffic cycle (red -> green -> yellow -> red). Which implementation is correct?

hard

A. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 30
case .yellow: return 5
case .green: return 25
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

B. enum Light {
case red, yellow, green

func time() -> Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
if self == .red { return .yellow }
else if self == .yellow { return .green }
else { return .red }
}
}

C. enum Light {
case red, yellow, green

var time: Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
switch self {
case .red: return .yellow
case .yellow: return .green
case .green: return .red
}
}
}

D. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 25
case .yellow: return 30
case .green: return 5
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

Solution

1. Step 1: Check computed property time values

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } correctly returns 30 for red, 5 for yellow, and 25 for green as required.

2. Step 2: Check next() method cycle order

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } cycles red -> green -> yellow -> red, matching the problem statement.

3. Final Answer:

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } -> Option A

4. Quick Check:

   Correct time values and cycle order = enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } [OK]

Hint: Match switch cases exactly to problem requirements [OK]

Common Mistakes:

• Mixing up time values for colors
• Incorrect next() cycle order
• Using func instead of computed property for time