WithState — easy state in Xcode previews

WithState.swift

import SwiftUI
extension View {
    public func withState<Value, V: View>(_ state: Value, @ViewBuilder content: @escaping (_ state: Binding<Value>) -> V) -> some View {
        modifier(WithStateModifier(state, content: content))
    }
}

public struct WithState<Value, V: View>: View {

    public init(_ value: Value, @ViewBuilder content builder: @escaping (_ state: Binding<Value>) -> V) {
        self.value = value
        self.builder = builder
    }
    
    private let value: Value
    private let builder: (_ state: Binding<Value>) -> V
    public var body: some View {
        withState(value, content: builder)
    }
}

struct WithStateModifier<Value, V: View>: ViewModifier {
    init(_ state: Value, @ViewBuilder content builder: @escaping (_ state: Binding<Value>) -> V) {
        _state = .init(wrappedValue: state)
        self.builder = builder
    }
    @State var state: Value
    private let builder: (_ state: Binding<Value>) -> V

    @MainActor func body(content: Content) -> V {
        return builder(.init(projectedValue: $state))
    }
}