问题
I'm figuring out Property Wrappers in Swift, but I seem to miss something.
This is how I wrote a property wrapper for a dependency injection framework we use:
@propertyWrapper
struct Inject<Value> {
var _value: Value
var wrappedValue: Value {
get {
return _value
}
set {
_value = newValue
}
}
init(_ container: Container = AppContainer.shared) {
do {
_value = try container.resolve(Value.self)
} catch let e {
fatalError(e.localizedDescription)
}
}
}
But when I use it in my class like below, I get a compile error. I've seen a lot of examples that to me do the exact same thing but probably there are some differences.
class X: UIViewController {
@Inject var config: AppConfiguration
....
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
config.johnDoSomething() // Compile error: 'AppConfiguration' is not convertible to 'AppConfiguration?'
}
}
I few days ago I came across a reference that Xcode had compile issues with Generic Property Wrappers, but I can't find it anymore. I'm not sure if that's relevant but maybe somebody on SO can help me out.
Using Xcode 11.3.1
As requested, hereby a reprex (one file in playground):
import UIKit
/// This class is only to mimick the behaviour of our Dependency Injection framework.
class AppContainer {
static let shared = AppContainer()
var index: [Any] = ["StackOverflow"]
func resolve<T>(_ type: T.Type) -> T {
return index.first(where: { $0 as? T != nil }) as! T
}
}
/// Definition of the Property Wrapper.
@propertyWrapper
struct Inject<Value> {
var _value: Value
var wrappedValue: Value {
get {
return _value
}
set {
_value = newValue
}
}
init(_ container: AppContainer = AppContainer.shared) {
_value = container.resolve(Value.self)
}
}
/// A very minimal case where the compile error occurs.
class X {
@Inject var text: String
init() { }
}
回答1:
Just dealing with your "reprex":
Change
@Inject var text: String
to
@Inject() var text: String
来源:https://stackoverflow.com/questions/59836661/compile-error-on-property-wrapper-in-swift-5-1