BuildOptional and buildEither in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an optional view using BuildOptional.

Swift

var body: some View {
    VStack {
        Text("Hello")
        [1] {
            Text("Optional View")
        }
    }
}

Drag options to blanks, or click blank then click option'

AbuildEither

BbuildOptional

CbuildBlock

DbuildArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using buildEither instead of buildOptional for optional views.

Using buildBlock which is for multiple views, not optional ones.

The buildOptional function is used to conditionally include a view when the optional content exists.

2fill in blank

medium

Complete the code to choose the first view in a conditional using BuildEither.

Swift

var body: some View {
    Group {
        [1].first(
            Text("First View"),
            Text("Second View")
        )
    }
}

Drag options to blanks, or click blank then click option'

AbuildEither

BbuildOptional

CbuildBlock

DbuildArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using buildOptional when two views are involved.

Using buildBlock which is for multiple views, not conditional choices.

buildEither is used to choose between two views, representing either the first or second option.

3fill in blank

hard

Fix the error in the code by choosing the correct builder function for an either-or view.

Swift

var body: some View {
    Group {
        [1].second(
            Text("Option A"),
            Text("Option B")
        )
    }
}

Drag options to blanks, or click blank then click option'

AbuildEither

BbuildBlock

CbuildOptional

DbuildArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using buildOptional which only handles optional views.

Using buildBlock which is for multiple views, not conditional choices.

The buildEither function correctly handles choosing the second view in an either-or scenario.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that uses buildOptional and buildEither.

Swift

let views = [
    "optional": [1](Text("Optional View")),
    "either": [2].first(Text("First"), Text("Second"))
]

Drag options to blanks, or click blank then click option'

AbuildOptional

BbuildBlock

CbuildEither

DbuildArray

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up buildBlock with buildOptional or buildEither.

Using buildArray which is for arrays, not conditionals.

buildOptional is used for the optional view, and buildEither is used to choose the first view in the either-or pair.

5fill in blank

hard

Fill all three blanks to build a dictionary with keys using buildEither and values using buildOptional.

Swift

let components = [
    [1].second("key1", "key2"): [2](Text("Value1")),
    [3].first("key3", "key4"): [2](Text("Value2"))
]

Drag options to blanks, or click blank then click option'

AbuildBlock

BbuildOptional

CbuildEither

DbuildArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using buildBlock for keys or values which is incorrect here.

Confusing buildArray with buildEither or buildOptional.

buildEither is used to select keys (either second or first), and buildOptional is used to wrap the values as optional views.

Practice

1. What is the main purpose of buildOptional in Swift's result builders?

easy

A. To choose between two code paths explicitly

B. To wrap optional code blocks so they can be included or skipped

C. To force unwrap optionals in code blocks

D. To create loops inside result builders

Solution

1. Step 1: Understand buildOptional's role

   buildOptional is designed to handle optional code blocks, allowing them to be included if present or skipped if nil.

2. Step 2: Compare with other builder functions

   buildEither chooses between two paths, but buildOptional specifically wraps optional code, making it flexible for optional UI parts.

3. Final Answer:

   To wrap optional code blocks so they can be included or skipped -> Option B

4. Quick Check:

   buildOptional wraps optionals = B [OK]

Hint: Remember: buildOptional handles optionals, buildEither picks sides [OK]

Common Mistakes:

• Confusing buildOptional with buildEither
• Thinking buildOptional forces unwrapping
• Assuming buildOptional creates loops

2. Which of the following is the correct syntax to use buildEither for choosing the first branch in a Swift result builder?

easy

A. buildEither(option: 1) { Text("First") }

B. buildEither(second: { Text("First") })

C. buildEither(first: { Text("First") })

D. buildEither(branch: .first, content: { Text("First") })

Solution

1. Step 1: Recall buildEither syntax

   The correct syntax uses named parameters first or second to specify the branch.

2. Step 2: Identify the correct usage

   buildEither(first: { Text("First") }) uses buildEither(first: { ... }), which matches the official Swift syntax for choosing the first branch.

3. Final Answer:

   buildEither(first: { Text("First") }) -> Option C

4. Quick Check:

   buildEither first branch = A [OK]

Hint: Use named parameters first or second with buildEither [OK]

Common Mistakes:

• Using incorrect parameter names like option or branch
• Confusing first and second parameters
• Trying to pass branch as enum instead of named argument

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

enum ResultBuilder {
  static func buildEither(first: String) -> String { "First: \(first)" }
  static func buildEither(second: String) -> String { "Second: \(second)" }
}

let result = ResultBuilder.buildEither(first: "Hello")
print(result)

medium

A. Compilation error

B. Second: Hello

C. Hello

D. First: Hello

Solution

1. Step 1: Identify which buildEither is called

   The code calls buildEither(first: "Hello"), so the first overload is used.

2. Step 2: Understand the returned string

   The first overload returns the string "First: Hello" which is printed.

3. Final Answer:

   First: Hello -> Option D

4. Quick Check:

   buildEither first branch returns "First: Hello" = A [OK]

Hint: Check which named parameter is used: first or second [OK]

Common Mistakes:

• Assuming second branch runs when first is called
• Expecting just the input string without prefix
• Thinking this causes a compile error

4. Given this Swift code snippet, what is the error and how to fix it?

struct Builder {
  @resultBuilder
  struct MyBuilder {
    static func buildEither(first: String) -> String { first }
    static func buildEither(second: String) -> String { second }
  }
}

let value = Builder.MyBuilder.buildEither(third: "Oops")

medium

A. Error: No 'third' parameter; fix by using 'first' or 'second'

B. Error: Missing return statement; fix by adding return

C. Error: buildEither cannot be static; remove static keyword

D. No error; code runs fine

Solution

1. Step 1: Identify the method call

   The code calls buildEither(third: "Oops"), but only first and second parameters exist.

2. Step 2: Understand the fix

   To fix, replace third with either first or second to match the defined overloads.

3. Final Answer:

   Error: No 'third' parameter; fix by using 'first' or 'second' -> Option A

4. Quick Check:

   buildEither only accepts first or second = C [OK]

Hint: Use only first or second parameters with buildEither [OK]

Common Mistakes:

• Trying to add unsupported parameter names
• Ignoring static keyword requirements
• Assuming code runs without error

5. How can you use buildOptional and buildEither together to conditionally build a SwiftUI view that shows "Logged In" if a user is logged in, "Guest" if not logged in but guest mode is enabled, and nothing otherwise?

hard

A. Use buildOptional to wrap guest mode view, and buildEither to choose between logged in and guest

B. Use buildEither to wrap guest mode view, and buildOptional to choose between logged in and guest

C. Use only buildOptional for all conditions

D. Use only buildEither for all conditions

Solution

1. Step 1: Understand the conditions

   We have three cases: logged in, guest mode, and neither. buildEither can choose between logged in and guest mode views.

2. Step 2: Use buildOptional for the third case

   The third case (neither) means no view, so wrap the guest mode view in buildOptional to include it only if guest mode is enabled.

3. Step 3: Combine both builders

   Use buildEither to select logged in or guest mode, and buildOptional to skip guest mode if disabled, resulting in no view if neither condition is true.

4. Final Answer:

   Use buildOptional to wrap guest mode view, and buildEither to choose between logged in and guest -> Option A

5. Quick Check:

   buildOptional wraps optional guest, buildEither picks logged in or guest = D [OK]

Hint: buildEither picks branches; buildOptional skips optional parts [OK]

Common Mistakes:

• Using buildEither alone for optional skipping
• Using buildOptional alone for branching
• Not handling the 'no view' case properly