Filtering arrays of enums (Haskell / Swift 1.2 / Swift 2.0 comparison)

filter_colors.hs

-- data structure for RGBA, RGB & CMYK colors
data Color = RGBA Float Float Float Float
           | RGB  Float Float Float
           | CMYK Float Float Float Float
           deriving (Eq, Ord, Show)

-- list of colors
colors = [ RGBA 0.1 0.1 0.5 0.2
         , RGBA 1 1 0 0.9
         , RGB 0.5 0.5 0
         , RGB 1 1 1
         , CMYK 1.0 1.0 0 0 ]

-- functions to filter color list by constructor
rgbas cols = [c| c@RGBA {} <- cols]
rgbs  cols = [c| c@RGB {} <- cols]
cmyks cols = [c| c@CMYK {} <- cols]

-- filter color list
rgbaOnly = rgbas colors
rgbOnly = rgbs colors
cmykOnly = cmyks colors

filter_colors_if_case.swift

// Swift 2.0

// enum for RGBA, RGB & CMYK colors
enum Color { // too much hassle to implement CustomStringConvertible Protocol
  case RGBA(R:Double, G:Double, B:Double, A:Double)
  case RGB(R:Double, G:Double, B:Double)
  case CMYK(C:Double, M:Double, Y:Double, K:Double)
}

// functions to filter color by constructor (using `if case`)
extension Color {
  var isRGBA : Bool {
    if case .RGBA = self {
      return true
    }
    return false
  }
  
  var isRGB : Bool {
    if case .RGB = self {
      return true
    }
    return false
  }
  
  var isCMYK : Bool {
    if case .CMYK = self {
      return true
    }
    return false
  }
}

// array of colors
let colors = [
  Color.RGBA(R: 0.5, G: 0.2, B: 0, A: 0.2),
  Color.RGBA(R: 0, G: 0.9, B: 1, A: 0.9),
  Color.RGB(R: 0.2, G: 1, B: 1),
  Color.RGB(R: 0.1, G: 0.1, B: 0.9),
  Color.CMYK(C: 1.0, M: 0, Y: 0, K: 0)]

// filter color list
colors.filter { $0.isRGBA }
colors.filter { $0.isRGB }
colors.filter { $0.isCMYK }

// An alternative is the following, which is truly terrible
var rgba:[Color] = []
for case let .RGBA(r, g, b, a) in colors {
  rgba.append(.RGBA(R:r, G:g, B:b, A:a))
}

filter_colors_switch.swift

// Swift 1.2

// enum for RGBA, RGB & CMYK colors
enum Color { // can't be bothered to implement Printable Protocol
    case RGBA(R:Double, G:Double, B:Double, A:Double)
    case RGB(R:Double, G:Double, B:Double)
    case CMYK(C:Double, M:Double, Y:Double, K:Double)
}

// functions to filter color by constructor (using `switch`)
extension Color {
    var isRGBA : Bool {
        switch self {
        case .RGBA : return true
        default : return false
        }
    }
    
    var isRGB : Bool {
        switch self {
        case .RGB : return true
        default : return false
        }
    }
    
    var isCMYK : Bool {
        switch self {
        case .CMYK : return true
        default : return false
        }
    }
}

// array of colors
let colors = [
    Color.RGBA(R: 0.5, G: 0.2, B: 0, A: 0.2),
    Color.RGBA(R: 0, G: 0.9, B: 1, A: 0.9),
    Color.RGB(R: 0.2, G: 1, B: 1),
    Color.RGB(R: 0.1, G: 0.1, B: 0.9),
    Color.CMYK(C: 1.0, M: 0, Y: 0, K: 0)]

// filter color list
colors.filter { $0.isRGBA }
colors.filter { $0.isRGB }
colors.filter { $0.isCMYK }