// Define it like this:
func itemView(@Binding _ user: User) -> some View { ... }
// Call it like this:
List($model.users) { $user in
itemView($_: $user) // 👈👈 🐞 Compiler error here: Extraneous argument label '$_:' in call
}
// omit parameter label call should work ...
// but as of Xcode Version 13.0 beta 4 (13A5201i), the above do not compile
// this works:
// Define it like this:
func itemView(@Binding user: User) -> some View { ... }
// Call it like this:
List($model.users) { $user in
itemView($user: $user)
}
// Or call it this way:
List($model.users, rowContent: itemView($user:)) // 👈👈 💥 this cause preview to crash, sim okay
import SwiftUI
struct User: Identifiable {
let id = UUID()
var name: String
var isContacted = false
}
final class Model: ObservableObject {
@Published var users: [User]
init(_ users: [User]) {
self.users = users
}
}
struct ContentView: View {
@EnvironmentObject private var model: Model
// 0) instead of the following, which works
// would like to extract the `rowContent` closure to a separate func
var bodyOG: some View {
List($model.users) { $user in
//
// 1) **** want to extract the following to a func itemView(...)
//
VStack {
HStack {
Text(user.name)
Spacer()
Toggle("User has been contacted", isOn: $user.isContacted)
.labelsHidden()
}
Text("Contacted: \(user.isContacted ? "Yes" : "No")")
}
}
}
// 2) I want this way
var body: some View {
// this does not work
// rowContent signature is <#T##(Binding<Data.Element>) -> RowContent#>
// List($model.users, rowContent: itemView) // Compile error: Cannot convert value of type '(User) -> some View' to expected argument type '(Binding<[User]>.Element) -> some View' (aka '(Binding<User>) -> some View')
// this also doesn't work
List($model.users) { $user in
itemView($user)
}
}
// 3) *** what's the correct thing to do here?
// what should the function signature be using SE-0293 syntax?
func itemView(@Binding _ user: User) -> some View { // Compile error: Property type 'Binding<[User]>.Element' (aka 'Binding<User>') does not match 'wrappedValue' type 'User'
VStack {
HStack {
Text(user.name)
Spacer()
Toggle("User has been contacted", isOn: $user.isContacted)
.labelsHidden()
}
Text("Contacted: \(user.isContacted ? "Yes" : "No")")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let data = [
User(name: "Larry"),
User(name: "Curly"),
User(name: "Moe")
]
ContentView()
.environmentObject(Model(data))
}
}
I don't have beta access to mess around with the new toys, but that seems weird. Since user is a Binding and the projectedValue of a Binding (which I think is what $user means) should give you the binding itself, I would expect $user to be a valid reference. Maybe I'm misunderstanding how it is supposed to work. My knowledge of Binding is mostly academic rather than practical.
The rowContent closure parameter is a Binding<User>. The magic happen with SE-0293: if you name the parameter as $user, which is still a Binding<User>, SE-0293 then defines user as $user.wrappedValue.
How to write a func for the rowContent closure? Seems to me this should work:
func itemView(_ user: Binding<User>) -> some View {
why is this compile error:
Property type 'Binding<[User]>.Element' (aka 'Binding<User>') does not match 'wrappedValue' type 'User'
AFAICT, you want to pass in Binding<User>, which is an API wrapper, and use a wrapped User on callee side. In that case, the function signature should look like this:
func itemView(@Binding _ user: User) -> some View {
// `_user` is `Binding<User>`
// `$user` is `Binding<User>`
// `user` is `User`
}
and the call site could look like this:
// `x` is `Binding<User>`
itemView($_: x)
Technically, you're passing the projectedValue when using this syntax. It is a little confusing in case of Binding because its projected value has the same type as the storage. Let's say we have a wrapper:
struct Storage {
var projectedValue: Projected
var wrappedValue: Wrapped
init(projectedValue: Projected) { ... }
init(wrappedValue: Wrapped) { ... }
}
and a function:
function a(@Storage x: ...) {
// `_x` is `Storage`
// `$x` is `Projected`
// `x` is `Wrapped`
}
Then you can to pass the storage's projected value or wrapped value. In both cases, the language uses the appropriate initializer to create a newStorage:
Does the compiler generate two different function signatures?
I was hoping to do this (So that I can avoid adding one extra closure and call itemView directly):
List($model.users, rowContent: itemView)
// Compile error: Cannot convert value of type '(User) -> some View' to expected argument type '(Binding<[User]>.Element) -> some View' (aka '(Binding<User>) -> some View')
but this does not compile. I wish there is something like this:
List($model.users, rowContent: itemView[use the $ version of this])
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Odd compiler error:
import SwiftUI
struct User: Identifiable {
let id = UUID()
var name: String
var isContacted = false
}
final class Model: ObservableObject {
@Published var users: [User]
init(_ users: [User]) {
self.users = users
}
}
struct ContentView: View {
@EnvironmentObject private var model: Model
var body: some View {
List($model.users) { $user in
itemView(user: $user) // 👈 very odd, no compile error here, but error over at the func definition!
itemView($user: $user) // change the previous line to this the error below goes away
}
}
// there is nothing wrong with this, but if the call site is wrong, compiler error here
// this erroneous error message makes to look like the func definition here is wrong, but it's fine
func itemView(@Binding user: User) -> some View { // 👈 why compile error here? => Property type 'Binding<User>' does not match 'wrappedValue' type 'User'
// fix the call site, this error goes away
EmptyView()
}
}
Property wrappers that declare an init(projectedValue:) initializer are inferred to be API-level wrappers. These wrappers become part of the function signature, and the property wrapper is initialized at the call-site of the function.
=======
Bug #1:itemView($_: $user) do not compile:
import SwiftUI
struct User: Identifiable {
let id = UUID()
var name: String
var isContacted = false
}
final class Model: ObservableObject {
@Published var users: [User]
init(_ users: [User]) {
self.users = users
}
}
struct ContentView: View {
@EnvironmentObject private var model: Model
var body: some View {
List($model.users) { $user in
itemView($_: $user) // 👈👈 🐞 Compiler error here: Extraneous argument label '$_:' in call
}
}
func itemView(@Binding _ user: User) -> some View {
EmptyView()
}
}
Bug #2: Xcode SwiftUI preview crash, run in sim is fine:
import SwiftUI
struct User: Identifiable {
let id = UUID()
var name: String
var isContacted = false
}
final class Model: ObservableObject {
@Published var users: [User]
init(_ users: [User]) {
self.users = users
}
}
struct ContentView: View {
@EnvironmentObject private var model: Model
var body: some View {
List($model.users, rowContent: itemView($user:)) // 👈👈 💥 this cause preview to crash
// this works:
List($model.users) { $user in
itemView($user: $user)
}
}
func itemView(@Binding user: User) -> some View {
EmptyView()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let data = [
User(name: "Larry"),
User(name: "Curly"),
User(name: "Moe")
]
ContentView()
.environmentObject(Model(data))
}
}
This one maybe problem with SwiftUI preview and how it interact with SE-0293.
Crash log
CompileDylibError: Failed to build ContentView.swift
Check the issue navigator for any compilation errors.
Apple Swift version 5.5 (swiftlang-1300.0.27.6 clang-1300.0.27.2)
While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "/Users/mateo/Library/Developer/Xcode/DerivedData/PreviewCrashForFuncWPropWrapperParam-dwnrppkkgaqzyibjpemqiooqvwqg/Build/Intermediates.noindex/Previews/PreviewCrashForFuncWPropWrapperParam/Intermediates.noindex/PreviewCrashForFuncWPropWrapperParam.build/Debug-iphonesimulator/PreviewCrashForFuncWPropWrapperParam.build/Objects-normal/x86_64/ContentView.2.preview-thunk.swift")
While silgen emitFunction SIL function "@$s36PreviewCrashForFuncWPropWrapperParam11ContentViewV0abcdefg1_a12Replacement_hI2_2E15__preview__body33_7817697A203B92A1C9DFE2D362513A75LLQrvg".
for getter for __preview__body (at /Users/mateo/Library/Developer/Xcode/DerivedData/PreviewCrashForFuncWPropWrapperParam-dwnrppkkgaqzyibjpemqiooqvwqg/Build/Intermediates.noindex/Previews/PreviewCrashForFuncWPropWrapperParam/Intermediates.noindex/PreviewCrashForFuncWPropWrapperParam.build/Debug-iphonesimulator/PreviewCrashForFuncWPropWrapperParam.build/Objects-normal/x86_64/ContentView.2.preview-thunk.swift:28:49)
While silgen closureexpr SIL function "@$s36PreviewCrashForFuncWPropWrapperParam11ContentViewV0abcdefg1_a12Replacement_hI2_2E15__preview__body33_7817697A203B92A1C9DFE2D362513A75LLQrvgAC04itemI04userQr7SwiftUI7BindingVyAA4UserVG_tFQOy_Qo_ANcACcfu_".
for expression at [/Users/mateo/Library/Developer/Xcode/DerivedData/PreviewCrashForFuncWPropWrapperParam-dwnrppkkgaqzyibjpemqiooqvwqg/Build/Intermediates.noindex/Previews/PreviewCrashForFuncWPropWrapperParam/Intermediates.noindex/PreviewCrashForFuncWPropWrapperParam.build/Debug-iphonesimulator/PreviewCrashForFuncWPropWrapperParam.build/Objects-normal/x86_64/ContentView.2.preview-thunk.swift:28:40 - line:28:55] RangeText="itemView($user:"
