A wrapper to create any number of arbitrary state variables using parameter packs for testing bindable values in a preview.

PreviewState.swift

import SwiftUI

struct PreviewState<each T, Content: View>: View {
    @State private var value: (repeat each T)
    var content: (Binding<(repeat each T)>) -> Content
    
    init(
        _ value: repeat each T,
        @ViewBuilder content: @escaping (Binding<(repeat each T)>) -> Content
    ) {
        self._value = State(initialValue: (repeat each value))
        self.content = content
    }
    
    var body: some View {
        content($value)
    }
}

#Preview {
    VStack {
        PreviewState(false) {
            Toggle("First Value", isOn: $0)
        }
        
        PreviewState(false, 1, 10.0) {
            Toggle("First Value", isOn: $0.0)
            
            Stepper("Second Value", value: $0.1, in: 0...5)
            
            Slider(value: $0.2, in: 0...100)
        }
    }
}