Change what print(Object) displays in Swift 2.0

Question

I am trying to make my class Digit display the num variable whenever print is called on that object, in Swift 2.0. I thought this might be done with a description variable, but no luck.

class Digit {

  var num: Int
  var x: Int
  var y: Int
  var box: Int
  var hintList: [Int] = []
  var guess: Bool = false

  var description: String {
    let string = String(num)
    return string
  }
}

Answer 1

It isn't enough to just add a description variable. You need to also state that your class conforms to CustomStringConvertible (formerly known as Printable in earlier Swift versions).

If you command click the print function, you find the following description.

Writes the textual representation of value, and an optional newline, into the standard output.

The textual representation is obtained from the value using its protocol conformances, in the following order of preference: Streamable, CustomStringConvertible, CustomDebugStringConvertible. If none of these conformances are found, a default text representation is constructed in an implementation-defined way, based on the type kind and structure.

The part of which that matters here being that objects passed to print are not checked for whether or not they have a description method, but instead checked for things like whether or not the conform to protocols like CustomStringConvertible which offer data to be printed.

That being said, all you need to do in this case is specify that your class conforms to CustomStringConvertible since you've already added a description variable. If you hadn't already added this, the compiler would complain because this protocol requires that the description variable be implemented.

class Digit: CustomStringConvertible {
    var num: Int
    var x: Int
    var y: Int
    var box: Int
    var hintList: [Int] = []
    var guess: Bool = false

    var description: String {
        let string = String(num)
        return string
    }
}