[SR-13896] Confusing error message when assigning an optional UIImage as a state property #57
Comments
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Here is a reduced reproducer @propertyWrapper
class A {
var wrappedValue: Int?
}
struct S {
let b: Bool
@A var a: Int?
init(a: Int?, b: Bool = false) {
self.a = a // 'self' used before all stored properties are initialized
self.b = b
}
}As far as I could see the problem is related to the fact that in this case @A is a class and the way self is implicit passed to the property wrapper in the assignment that is required to all properties being initialized. init(image: UIImage?, asPreview: Bool = false) {
self.asPreview = asPreview // Make sure this is initialized before call property wrapper
self.image = image
}cc @hborla |
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This is a known issue where out-of-line initialization via wrapped value isn't supported for class property wrappers and struct property wrappers with nonmutating setters (due to limitations of the assign_by_wrapper instruction in SIL). Here's a reproducer without SwiftUI: @propertyWrapper
struct State<Value> {
private var _wrappedValue: Value
var wrappedValue: Value {
get { _wrappedValue }
nonmutating set {}
}
init(wrappedValue: Value) {
_wrappedValue = wrappedValue
}
}
struct BookView {
let flag: Bool
@State var str: String
init(str: String, flag: Bool = false) {
self.str = str
self.flag = flag
}
}@LucianoPAlmeida you're right that the error message should make it clear how to fix the issue. The right fix is to initialize the backing property wrapper directly, e.g.: init(str: String, flag: Bool = false) {
self._str = State(wrappedValue: str)
self.flag = flag
} |
Attachment: Download
Environment
macOS Catalina 10.15.7
Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1)
Xcode 12.1
Additional Detail from JIRA
md5: f20a4f1b3d227c0ef91b2fdd21421924
Issue Description:
I'm working on project that uses both UIKit and SwiftUI and I found a scenario that shows a confusing error when assigning a `UIImage?` in a struct initializer. The error is:
And this is the code that produces the error:
The error is pointed in line 9 right under the equal sign ("self.image = image"), but actually that line assigns a different struct property, so it's a little bit confusing.
What it could be happening is that a different type of value is being assigned to the image variable, so the error message that should be shown instead could be something related of assigning an `UIImage?` to a `State<UIImage?>` variable.
The code above can be used in Xcode playground to reproduce the issue. I've attached a screenshot reproducing the bug.
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