Implementing copy() in Swift

Question

I want to be able to copy a custom class in Swift. So far, so good. In Objective-C I just had to implement the NSCopying protocol, which means implementing

Answer 1

IMO, the simplest way to achieve this is :

protocol Copyable
{
  init(other: Self)
}

extension Copyable
{
  func copy() -> Self
  {
    return Self.init(other: self)
  }
}

Implemented in a struct as :

struct Struct : Copyable
{
  var value: String

  init(value: String)
  {
    self.value = value
  }

  init(other: Struct)
  {
    value = other.value
  }
}

And, in a class, as :

class Shape : Copyable
{
  var color: NSColor

  init(color: NSColor)
  {
    self.color = color
  }

  required init(other: Shape)
  {
    color = other.color
  }
}

And in subclasses of such a base class as :

class Circle : Shape
{
  var radius: Double = 0.0

  init(color: NSColor, radius: Double)
  {
    super.init(color: color)

    self.radius = radius
  }

  required init(other: Shape)
  {
    super.init(other: other)

    if let other = other as? Circle
    {
      radius = other.radius
    }
  }
}


class Square : Shape
{
  var side: Double = 0.0

  init(color: NSColor, side: Double)
  {
    super.init(color: color)

    self.side = side
  }

  required init(other: Shape)
  {
    super.init(other: other)

    if let other = other as? Square
    {
      side = other.side
    }
  }
}

If you want to be able to copy an array of Copyable types :

extension Array where Element : Copyable
{
  func copy() -> Array
  {
    return self.map { $0.copy() }
  }
}

Which then allows you to do simple code like :

{
  let shapes = [Circle(color: .red, radius: 5.0), Square(color: .blue, side: 5.0)]

  let copies = shapes.copy()
}