This resolves another small but potentially annoying inconsistency in Swift where downcasting a collection – e.g. casting an array of ClassA
to an array of another type that inherits from ClassA
– would not be allowed in some circumstances.
For example, this code is now valid in Swift 5.8, whereas it would not have worked previously:
class Pet { }
class Dog: Pet {
func bark() { print("Woof!") }
}
func bark(using pets: [Pet]) {
switch pets {
case let pets as [Dog]:
for pet in pets {
pet.bark()
}
default:
print("No barking today.")
}
}
Before Swift 5.8 that would have led to the error message, “Collection downcast in cast pattern is not implemented; use an explicit downcast to '[Dog]' instead.” In practice, syntax such as if let dogs = pets as? [Dog] {
worked just fine, so I would imagine that error was rarely seen. However, this change does mean another language inconsistency is resolved, which is always welcome.
SPONSORED Transform your career with the iOS Lead Essentials. Unlock over 40 hours of expert training, mentorship, and community support to secure your place among the best devs. Click for early access to this limited offer and a FREE crash course.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Download all Swift 5.8 changes as a playground Link to Swift 5.8 changes
Link copied to your pasteboard.