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.
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Other changes in Swift 5.8…
- Lift all limitations on variables in result builders
- Function back deployment
- Allow implicit self for weak self captures, after self is unwrapped
- Concise magic file names
- Opening existential arguments to optional parameters
Download all Swift 5.8 changes as a playground Link to Swift 5.8 changes
