The assignment operation of struct variable with inner reference.

StructWithInnerReference.swift

// Inner Reference Type 
final internal class CoWInnerClass {
  var identifier: Int
  init(_ id: Int) {
    identifier = id
  }
}

// The struct with inner reference type.
struct CoWValueWithRef: CustomStringConvertible {
  let ref1 = CoWInnerClass(1)
  let ref2 = CoWInnerClass(2)
  var description: String {
    return String("ref1: \(ObjectIdentifier(ref1)) ref2: \(ObjectIdentifier(ref2))")
  }
}

// The test case function
private func testValueWithRef() {
  let valueWithRef1 = CoWValueWithRef()
  // The assignment operation
  let valueWithRef2 = valueWithRef1
  // Another struct variable
  let valueWithRef3 = CoWValueWithRef()
  print("valueWithRef1: \(valueWithRef1)")
  print("valueWithRef2: \(valueWithRef2)")
  print("valueWithRef3: \(valueWithRef3)")
}

/*
------------------------
Output from console is as the following:
valueWithRef1: ref1: ObjectIdentifier(0x00006000039e9780) ref2: ObjectIdentifier(0x00006000039e9740)
valueWithRef2: ref1: ObjectIdentifier(0x00006000039e9780) ref2: ObjectIdentifier(0x00006000039e9740)
valueWithRef3: ref1: ObjectIdentifier(0x00006000039e9860) ref2: ObjectIdentifier(0x00006000039e9880)
*/