struct User {struct User {    var firstName = "Bilbo"    var lastName = "Baggins"}
struct ContentView: View {    @State private var user = User()  //1
    var body: some View {        VStack {            Text("Your name is \(user.firstName) \(user.lastName).")  //2            TextField("First name", text: $user.firstName) //3            TextField("Last name", text: $user.lastName)        }    }}

struct User {struct User {    var name:String    mutating func changeName(name:String) {        self.name = name    }}

//Modelstruct Product:Identifiable {    var isFavorited:Bool    var title:String    var id: String}//SubViewstruct FilterView: View {    @Binding var showFavorited: Bool  //3
    var body: some View {        Toggle(isOn: $showFavorited) {  //4            Text("Change filter")        }    }}//ParentViewstruct ProductsView: View {    let products: [Product] = [    Product(isFavorited: true, title: "ggggg",id: "1"),    Product(isFavorited: false, title: "3333",id: "2")]
    @State private var showFavorited: Bool = false   //1
    var body: some View {        List {            FilterView(showFavorited: $showFavorited)  //2
            ForEach(products) { product in                if !self.showFavorited || product.isFavorited {                    Text(product.title)                }            }        }    }}

struct StateMutableView: View {struct StateMutableView: View {    @State private var flag = false  //flag是标记为State的变量    private var anotherFlag = false  //anotherFlag是没有使用属性包装器的普通变量
    mutating func changeAnotherFlag(_ value: Bool) {  //mutating的方法修改anotherFlag        self.anotherFlag = value    }        var body: some View {        Button(action: {            //1 ok            self.flag = true                        //2 Cannot assign to property: 'self' is immutable            self.anotherFlag = true                        //3 Cannot use mutating member on immutable value: 'self' is immutable            changeAnotherFlag(true)        }) {            Text("Test")        }    }}

struct SimpleStruct {struct SimpleStruct {    //计算属性anotherFlag    var anotherFlag: Bool {        _anotherFlag = true//      ^~~~~~~~~~~~//      error: cannot assign to property: 'self' is immutable        return _anotherFlag    }    //存储属性_anotherFlag    private var _anotherFlag = false}

struct SimpleStruct {struct SimpleStruct {    var anotherFlag: Bool {        mutating get {            _anotherFlag = true            return _anotherFlag        }    }
    private var _anotherFlag = false}

var s0 = SimpleStruct()_ = s0.anotherFlag // ok, and modifies s0let s1 = SimpleStruct()_ = s1.anotherFlag// ^~ error: cannot use mutating getter on immutable value: 's1' is a 'let' constant

public protocol View {
    /// The type of view representing the body of this view.    ///    /// When you create a custom view, Swift infers this type from your    /// implementation of the required `body` property.    associatedtype Body : View
    /// Declares the content and behavior of this view.    var body: Self.Body { get }}

struct SimpleView: View {//     ^ error: type 'SimpleView' does not conform to protocol 'View'     var body: some View {        mutating get { Text("Hello") }    }}

@frozen @propertyWrapper public struct State<Value> : DynamicProperty {
    /// Initialize with the provided initial value.    public init(wrappedValue value: Value)
    /// Initialize with the provided initial value.    public init(initialValue value: Value)
    /// The current state value.    public var wrappedValue: Value { get nonmutating set }
    /// Produces the binding referencing this state value    public var projectedValue: Binding<Value> { get }}

struct SimpleStruct {    var anotherFlag: Bool {        mutating get {            _anotherFlag = true            return _anotherFlag        }    }
    private var _anotherFlag: Bool {        get {            return UserDefaults.standard.bool(forKey: "storage")        }        nonmutating set {            UserDefaults.standard.setValue(newValue, forKey: "storage")        }    }}
let s0 = SimpleStruct()var s1 = s0_ = s1.anotherFlag // 同时影响s0和s1，他们内部的_anotherFlag都发生了变化

po self▿ User \- name : "" \- count : 0

po self▿ ContentView ▿ _user : State<User>  ▿ _value : User   \- name : ""   \- count : 0  \- _location : nil

_user = State(wrappedValue: User(name: "TT", count: 100))

User initContentView init140732783334216▿ SwiftUI.State<DemoState.User>  ▿ _value: DemoState.User    - name: ""    - count: 0  - _location: nil

po self▿ ContentView  ▿ _user : State<User>    ▿ _value : User      - name : ""      - count : 0    ▿ _location : Optional<AnyLocation<User>>      ▿ some : <StoredLocation<User>: 0x600003c26a80>

140732783330824▿ SwiftUI.State<DemoState.User>  ▿ _value: DemoState.User    - name: ""    - count: 0  ▿ _location: Optional(SwiftUI.StoredLocation<DemoState.User>)    ▿ some: SwiftUI.StoredLocation<DemoState.User> #0

(lldb) p _user(State<DemoState.User>) $R6 = {  _value = (name = "", count = 2)  _location = 0x0000600003c26a80 {    SwiftUI.AnyLocationBase = {}  }}
(lldb) p _user.wrappedValue(DemoState.User) $R8 = (name = "", count = 2)
(lldb) p _user.projectedValue(Binding<DemoState.User>) $R10 = {  transaction = {    plist = {      elements = nil    }  }  location = 0x0000600003c26a80 {    SwiftUI.AnyLocationBase = {}  }  _value = (name = "", count = 2)}

private var _user: State<User> = State(initialValue: User())private var $user: Binding<User> { return _user.projectedValue }private var user: User {    get { return _user.wrappedValue }    nonmutating set { _user.wrappedValue = newValue }}

(lldb) expr $user = User(name:"",count:100)error: <EXPR>:3:1: error: cannot assign to property: '$user' is immutable$user = User(name:"",count:100)^~~~~error: <EXPR>:3:9: error: cannot assign value of type 'User' to type 'Binding<User>'$user = User(name:"",count:100)^~~~~~~~~~~~~~~~~~~~~~~(lldb) expr $user.name = "Tim"error: <EXPR>:3:7: error: cannot assign to property: '$user' is immutable$user.name = "Tim"~~~~~ ^error: <EXPR>:3:14: error: cannot assign value of type 'String' to type 'Binding<String>'$user.name = "Tim"^~~~~

_user:State<User>	_value:User		_name:String		_count:Int	_wrappedValue:User 		get { _value }		set { _value = newValue }	_projectedValue:User 		get { _value }

@propertyWrapper struct State<T> {    var _value:T        init(wrappedValue: T) {        _value = wrappedValue    }
    var wrappedValue: T {        nonmutating set { _value = newValue }           get { _value.value }    }
    var projectedValue: T { _value }}