Why result builders enable DSLs in Swift - See It in Action

Why result builders enable DSLs

📖 Scenario: Imagine you want to create a simple way to build HTML code using Swift. Writing HTML tags by hand can be long and confusing. Result builders help you write HTML in a clean, easy style that looks like a mini language inside Swift.

🎯 Goal: You will build a small HTML builder using Swift's result builders. This will show how result builders let you create your own little language (DSL) inside Swift code.

📋 What You'll Learn

Create a simple data structure to hold HTML content

Define a result builder called HTMLBuilder

Use the result builder to build HTML tags in a clean way

Print the final HTML string

💡 Why This Matters

🌍 Real World

Result builders let developers write code that looks like a small language inside Swift. This makes building UI, HTML, or other structured data easier and clearer.

💼 Career

Understanding result builders helps you work with SwiftUI and other modern Swift frameworks that use DSLs for clean, readable code.

1

Create a struct called HTML with a content string

Create a struct called HTML with one property content of type String. Add an initializer that sets content.

Swift

struct HTML {
    // Your code here
}

Need a hint?

Use struct to create HTML. Add a property content and an initializer that takes a String.

2

Define a result builder called HTMLBuilder

Define a result builder called HTMLBuilder using @resultBuilder. Add a static function buildBlock that takes multiple HTML parameters and returns a single HTML by joining their content strings.

Swift

struct HTML {
    let content: String
    init(_ content: String) {
        self.content = content
    }
}

// Define the result builder here
// Your code here

Need a hint?

Use @resultBuilder before struct HTMLBuilder. The buildBlock function combines all HTML contents into one.

3

Create a function html using HTMLBuilder to build HTML content

Create a function called html that takes a closure marked with @HTMLBuilder and returns HTML. Inside the function, call the closure and return its result.

Swift

struct HTML {
    let content: String
    init(_ content: String) {
        self.content = content
    }
}

@resultBuilder
struct HTMLBuilder {
    static func buildBlock(_ components: HTML...) -> HTML {
        let combined = components.map { $0.content }.joined(separator: "")
        return HTML(combined)
    }
}

// Create the html function here
// Your code here

Need a hint?

Define html with a closure parameter marked @HTMLBuilder. Return the result of calling the closure.

4

Use the html function to build and print HTML content

Use the html function to build HTML with two tags: HTML("

Hello

") and HTML("

Welcome to DSLs!

"). Store the result in page. Then print page.content.

Swift

struct HTML {
    let content: String
    init(_ content: String) {
        self.content = content
    }
}

@resultBuilder
struct HTMLBuilder {
    static func buildBlock(_ components: HTML...) -> HTML {
        let combined = components.map { $0.content }.joined(separator: "")
        return HTML(combined)
    }
}

func html(@HTMLBuilder content: () -> HTML) -> HTML {
    return content()
}

// Build the HTML page and print the content
// Your code here

Need a hint?

Call html with two HTML lines inside. Print the combined content.