[Idea] Find alternatives to `switch self`

Evolution Discussion
1

Maybe the dictionary literal syntax could be used as a shorthand?

enum Suit: Int {
  case Hearts, Spades, Diamonds, Clubs
  
  var description: String {
    return switch self [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ]
  }
  
  var isRed: Bool {
    return switch self [
      .Hearts: true,
      .Diamonds: true,
      .Spades: false,
      .Clubs: false
    ]
  }
}

Patrick

2

This can be done today with no syntax changes (you'd have to return
optional or handle the nil case though):

  var description: String? {
    return [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ][self]
  }

···

On 3/23/2016 8:42 PM, Patrick Smith via swift-evolution wrote:

Maybe the dictionary literal syntax could be used as a shorthand?

enum Suit: Int {
  case Hearts, Spades, Diamonds, Clubs

  var description: String {
    return switch self [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ]
  }

  var isRed: Bool {
    return switch self [
      .Hearts: true,
      .Diamonds: true,
      .Spades: false,
      .Clubs: false
    ]
  }
}

Patrick

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3

You could always use nil-coalescing

    return [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ][self ] ?? "won't happen"

Or do something silly like this:

public extension Dictionary {
    public subscript(key: Key, fallback: Value) -> Value {
        return self[key] ?? fallback
    }
}

enum Suits {
    case Hearts, Spades, Diamonds, Clubs
    var description: String {
        let values: [Suits: String] = [
            .Hearts: ":heart:",
            .Spades: ":spades:",
            .Diamonds: ":diamonds:",
            .Clubs: ":clubs:"
            ]
        return values[self, "?"]
    }
}

Even thought they kind of sort of work, I don't like either one.

-- E

···

On Mar 23, 2016, at 9:23 PM, Kevin Lundberg via swift-evolution <swift-evolution@swift.org> wrote:

This can be done today with no syntax changes (you'd have to return optional or handle the nil case though):

  var description: String? {
    return [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ][self]
  }

4

This can be done today with no syntax changes (you'd have to return optional or handle the nil case though):

  var description: String? {
    return [
      .Hearts: ":heart:",
      .Spades: ":spades:",
      .Diamonds: ":diamonds:",
      .Clubs: ":clubs:"
    ][self]
  }

"You have to handle the nil case" is a symptom of the real problem with this approach: you lose exhaustiveness checking.

···

--
Brent Royal-Gordon
Architechies

1 Like