How does SwiftUI's diffing algorithm work?

Answer: SwiftUI compares the new view tree with the previous one on every state change. It uses the structural identity of views (their type and position in the hierarchy) to determine what changed and only re-renders the minimum necessary.

Key Points:

• Views are value types — SwiftUI compares them cheaply
• Identity is determined by position and type, not by reference
• Using id() modifier lets you override identity — changing id destroys and recreates the view
• equatable() modifier lets you skip re-renders when inputs haven't changed

Code Example:

// SwiftUI only re-renders views whose inputs changed
struct ParentView: View {
    @State private var count = 0

    var body: some View {
        VStack {
            CounterView(count: count)  // re-renders when count changes
            StaticLabel()              // never re-renders — no dependencies
        }
    }
}

// Force recreation when id changes (e.g. reset a text field)
TextField("Name", text: $name)
    .id(resetToken)  // change resetToken to fully recreate