Is there a way to swap two different objects in Swift

Question

I am wondering if there is a way to swap two objects of different types in Swift.

Here is my trial:

func swapXY<T>(inout first: T,intout second: T)
{
    (first ,second  ) = ( second,  first)
}

Let's say I want the two parameters to be T,Y respectively. How can this be accomplished?

Answer 1

Yes you can swap two items, and the function is already included in the standard library.

swap(_:_:)

Exchange the values of a and b.
Declaration

func swap<T>(inout _ a: T, inout _ b: T)

Swift Standard Library Functions Reference

However, if they are not the same type, then no, you cannot swap two items of different types.

Swift 3

func swap<swapType>( _ a: inout swapType, _ b: inout swapType) {
  (a, b) = (b, a)
}

Answer 2

What you can do is a much more specific swap of classes inheriting from a common ancestor:

class Animal {}
class Dog: Animal {}
class Cat: Animal {}

// Note that cat and dog are both variables of type `Animal`, 
// even though their types are different subclasses of `Animal`.
var cat: Animal = Cat()
var dog: Animal = Dog()

print("cat: \(cat)")
print("dog: \(dog)")

swap(&dog, &cat) // use the standard Swift swap function.

print("After swap:")
print("cat: \(cat)")
print("dog: \(dog)")

The above code works because cat and dog are both "is-a" Animal, both before and after the swap. Swapping objects of unrelated types, however, cannot be done in Swift, nor does it really make sense:

var dog = Dog() // dog is of type Dog, NOT Animal
var cat = Cat() // cat is of type Cat, NOT Animal
swap(&cat, &dog) // Compile error!

This code won't compile because a variable of type Dog cannot hold a value of type Cat in Swift or any other strongly-typed language.