Protocol requirements specialization

Using Swift
,
9

The full sample code is as follows:

protocol Animal {
  func greet(_ animal: some Animal)
  func _greetedByDog(_ dog: Dog)
}

extension Animal {
  func greet<A: Animal>(_ animal: A) {
    print("\(Self.self) sniffs \(A.self) cautiously")
  }

  func _greetedByDog(_ dog: Dog) {
    print("\(Dog.self) sniffs \(Self.self) cautiously")
  }
}

struct Cat: Animal {}
struct Dog: Animal {
  func greet(_ animal: some Animal) {
    animal._greetedByDog(self)
  }

  func _greetedByDog(_ dog: Dog) {
    print("Bark in excitement")
  }
}

func walk<each A: Animal>(_ animals: repeat each A, towards animal: some Animal) {
  repeat (each animals).greet(animal)
}

If we do the same test as last time:

walk(Cat(), Dog(), towards: Dog())

We get:

Cat sniffs Dog cautiously
Bark in excitement
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