Example of how init/func behaves in protocols and protocol extensions

InitInProtocol.swift

protocol P1 {
  init()
  func bar()
}
extension P1 {
  init() {
    self.init()
    print("P1 init")
  }
  func bar() {
    print("P1 func")
  }
}
struct S1: P1 {
  init() {
    print("S1 init")
  }
  func bar() {
    print("S1 func")
  }
}

protocol P2 {}

extension P2 {
  init() {
    self.init()
    print("P2 init")
  }
  func bar() {
    print("P2 func")
  }
}
struct S2: P2 {
  init() {
    print("S2 init")
  }
  func bar() {
    print("S2 func")
  }
}

let s1 = S1() // prints "S1 init"
s1.bar()      // prints "S1 func"

let s2 = S2() // prints "S2 init"
s2.bar()      // prints "S2 func"