ios - Fatal error: could not demangle keypath type

Question

I have a simple class and I want to use keypath in the init, something like this:

class V: UIView {
    convenience init() {
        self.init(frame: .zero)
        self[keyPath: \.alpha] = 0.5
    }
}

let v = View()

When I run this code I get a runtime error:

Fatal error: could not demangle keypath type from ' ����XD':

But, if I specify the type in keyPath it works fine:

class V: UIView {
    convenience init() {
        self.init(frame: .zero)
        self[keyPath: \UIView.alpha] = 0.5
    }
}

let v = View()
print(v.alpha) \\ prints 0.5

But, what's even stranger is that this code works:

class V: UIView {
    convenience init() {
        self.init(frame: .zero)
        foo()
    }
    
    func foo() { 
        self[keyPath: \.alpha] = 0.5
    }
}

let v = View()
print(v.alpha) \\ prints 0.5

What is the actual reason for this error?

标签： iosswiftuikitswift5.1swift-keypath

Answer 1