ios – Why does the view’s internal state is not updated for first mutation when doing it via an Computed Binding

Attaching the demo code:

import SwiftUI

struct BufferTest: View {
    @Binding var text: String
    @State private var buffer: String = ""

    @State private var presentModificationSheet: Bool = false

    var bufferedBinding: Binding {
        Binding {
            text
        } set: {
            buffer = $0
            if text != buffer {
                presentModificationSheet = true
            }
        }
    }

    var body: some View {
        Text("Binding: \(text)")
//        Text("Buffer: \(buffer)")

        InternalModder(binding: bufferedBinding)
            .sheet(isPresented: $presentModificationSheet) {
                TerminalSheet(text: $text, buffer: buffer)
            }

    }

    struct InternalModder: View {
        @Binding var binding: String

        var body: some View {
            Button("Set") { binding = "New Value" + (1...10).randomElement()!.formatted() }
        }
    }
    
    struct TerminalSheet: View {
        @Binding var text: String
        var buffer: String
        
        var body: some View {
            Text("Binding: \(text)")
            Text("Buffer: \(buffer)")
            Button("Update") { text = buffer }
        }
    }
}

@available(iOS 17.0, *)
#Preview {
    @Previewable @State var text = ""

    BufferTest(text: $text)
}

Here, when pressing the button “Set” for first time, the sheet is presented but does not have the updated buffered value. However, mutations after that takes place correctly.

If we uncomment the

Text("Buffer: \(buffer)")

within BufferTest’s body, then the updates are taking place correctly.

Why does this happen ? and if it is the intended behavior, mutating like this isn’t recommended ?

Also the straightforward way to solve this is via onChange modifier:

.onChange(of: buffer) { new in
    if new != text {
        presentModificationSheet = true
    }
}