BuildBlock for combining results in Swift - Mini Project: Build & Apply

BuildBlock for combining results

📖 Scenario: You are creating a simple Swift program that combines results from multiple operations using a buildBlock function. This is useful when you want to gather multiple values into one combined result.

🎯 Goal: Build a Swift function using @resultBuilder with a buildBlock method that combines multiple String results into one concatenated String. Then use this builder to combine several strings and print the final combined string.

📋 What You'll Learn

Create a @resultBuilder struct named StringCombiner with a static buildBlock method that takes multiple String parameters and returns their concatenation.

Create a function combineStrings that uses @StringCombiner to combine multiple strings.

Call combineStrings with three specific strings: "Hello, ", "Swift ", and "World!".

Print the combined result.

💡 Why This Matters

🌍 Real World

Result builders in Swift help combine multiple pieces of data or code blocks into one result, making code cleaner and easier to read, especially in UI building or DSLs.

💼 Career

Understanding result builders is useful for Swift developers working on SwiftUI, server-side Swift, or any code that benefits from declarative syntax and combining multiple values.

1

Create the @resultBuilder struct

Create a @resultBuilder struct called StringCombiner with a static method buildBlock that takes a variable number of String parameters and returns a single String by concatenating them.

Swift

# Your code here

Need a hint?

Use @resultBuilder before the struct. The buildBlock method should join all strings in components.

2

Create the combineStrings function using StringCombiner

Create a function called combineStrings that uses the @StringCombiner attribute. This function should return a String and accept a closure that returns multiple String values.

Swift

@resultBuilder
struct StringCombiner {
    static func buildBlock(_ components: String...) -> String {
        components.joined(separator: "")
    }
}

// Your code here

Need a hint?

Use @StringCombiner before the function and the closure parameter. Return the result of calling content().

3

Call combineStrings with three strings

Call the function combineStrings with a closure that returns these exact strings in order: "Hello, ", "Swift ", and "World!".

Swift

@resultBuilder
struct StringCombiner {
    static func buildBlock(_ components: String...) -> String {
        components.joined(separator: "")
    }
}

@StringCombiner
func combineStrings(@StringCombiner _ content: () -> String) -> String {
    content()
}

// Your code here

Need a hint?

Call combineStrings with a closure containing the three strings on separate lines.

4

Print the combined result

Print the variable result to display the combined string.

Swift

@resultBuilder
struct StringCombiner {
    static func buildBlock(_ components: String...) -> String {
        components.joined(separator: "")
    }
}

@StringCombiner
func combineStrings(@StringCombiner _ content: () -> String) -> String {
    content()
}

let result = combineStrings {
    "Hello, "
    "Swift "
    "World!"
}

// Your code here

Need a hint?

Use print(result) to show the combined string.