TL;DR #

@ViewBuilder is SwiftUI’s specialized result builder that collects multiple view expressions and control-flow statements into a single, efficient some View return value—letting you write clean, declarative UI without manual container nesting.

What Is a Result Builder? #

Starting in Swift 5.4, Swift introduced the general-purpose @resultBuilder feature (formerly “function builders”). A result builder transforms a sequence of statements in a closure into a single value. SwiftUI leverages this to define @ViewBuilder, which:

• Collects multiple View expressions
• Transforms them into a single some View via tuples or specialized container types
• Handles control flow (if/else, switch, for loops) seamlessly

Under the hood, the compiler rewrites your closure into calls like:

public struct ViewBuilder {
  static func buildBlock<Content>(_ views: Content...) -> TupleView<Content> { … }
  static func buildIf<Content>(_ content: Content?) -> Content? { … }
  static func buildEither<True, False>(first: True) -> EitherView<True, False> { … }
  static func buildEither<True, False>(second: False) -> EitherView<True, False> { … }
  static func buildArray<Content>(_ components: [Content]) -> ForEach<…> { … }
}

When you write:

@ViewBuilder
var body: some View {
    Text("A")
    if showExtra {
        Text("B")
    }
    ForEach(items) { item in
        Text(item.name)
    }
}

The compiler automatically invokes buildBlock, buildIf, buildEither, and buildArray to assemble a nested structure (TupleView, EitherView, ForEach) that SwiftUI can diff and render efficiently.

Why @ViewBuilder Matters in SwiftUI #

1. Eliminates Manual Container Wrapping #

Without @ViewBuilder, you’d need to explicitly nest every view and branch:

var body: some View {
    Group {
        VStack {
            Text("A")
            if showExtra {
                Text("B")
            }
            VStack {
                ForEach(items) { item in
                    Text(item.name)
                }
            }
        }
    }
}

With @ViewBuilder, that boilerplate vanishes—your closure’s sequence is grouped for you.

2. Supports Conditional and Loop Logic Natively #

You get first-class if/else, switch, and for support directly in your view declarations:

@ViewBuilder
var dynamicBody: some View {
    Text("User List")
    if users.isEmpty {
        Text("No users found")
    } else {
        ForEach(users) { user in
            UserRow(user: user)
        }
    }
}

Each branch becomes an EitherView, so SwiftUI knows exactly which path to render—and can diff changes cleanly.

3. Improves Readability by Modeling Your Intent #

• Linear, top-to-bottom syntax instead of nested brackets
• Clear control flow without extra containers
• Focus on what to display, not how to assemble it

Your code reads like your UI spec, making onboarding and maintenance much smoother.

4. Reduces Boilerplate and Enables Optimizations #

By capturing your view tree in a typed, compile-time structure, SwiftUI can:

• Diff only changed subviews, avoiding full reloads
• Flatten nested tuples and groups
• Specialize layout passes per container, improving performance

All thanks to the compiler-generated combiners (TupleView, Group, EitherView, etc.) that result builders produce.

Takeaways #

• @ViewBuilder is simply SwiftUI’s @resultBuilder for building View hierarchies.
• It removes manual container wrapping, supports control flow inline, and yields code that’s both readable and efficient.