Swiftui how to pass an optioanl value to Binding

refer to SwiftUI Optional TextField

import SwiftUI

func ??<T>(lhs: Binding<Optional<T>>, rhs: T) -> Binding<T> {
    Binding(
        get: { lhs.wrappedValue ?? rhs },
        set: { lhs.wrappedValue = $0 }
    )
}

then:

TextField("", text: $test ?? "default value")