code / tomo-koans

   1 # Enums
   2 
   3 # Enums define a type with multiple possible variants:
   4 enum Shape(Circle(radius: Num), Rectangle(width: Num, height: Num), Point)
   5 
   6     # Use `when` to pattern match an enum:
   7     func area(shape: Shape -> Num)
   8         when shape is Circle(radius)
   9             return Num.PI * radius^2
  10         is Rectangle(width, height)
  11             return width * height
  12         is Point
  13             return 0
  14 
  15 func main()
  16 
  17     # You can create instances of an enum:
  18     point := Shape.Point
  19 
  20     # Single member enums display without the field names:
  21     circle := Shape.Circle(radius=10)
  22     assert circle == Shape.Circle(10)
  23 
  24     # Multi-member enums explicitly list their field names:
  25     rect := Shape.Rectangle(width=4, height=5)
  26     assert rect == Shape.Rectangle(width=4, height=5)
  27 
  28     assert point.area() == ???
  29 
  30     assert rect.area() == ???
  31 
  32     assert "My shape is $circle" == ???