2.4.2 Using enums

Enums are a good choice if only a finite set of values should be allowed. The individual constructors then represent the allowed variants and enable the compiler to check if all possible values are respected. This can be seen here:

enum Color {
  Red;
  Green;
  Blue;
  Rgb(r:Int, g:Int, b:Int);
}

class Main {
  static function main() {
    var color = getColor();
    switch (color) {
      case Red: trace("Color was red");
      case Green: trace("Color was green");
      case Blue: trace("Color was blue");
      case Rgb(r, g, b): trace("Color had a red value of " +r);
    }
  }

  static function getColor():Color {
    return Rgb(255, 0, 255);
  }
}

After retrieving the value of color by assigning the return value of getColor() to it, a switch expression is used to branch depending on the value. The first three cases Red, Green and Blue are trivial and correspond to the constructors of Color that have no arguments. The final case Rgb(r, g, b) shows how the argument values of a constructor can be extracted: they are available as local variables within the case body expression, just as if a var expression had been used.

Advanced information on using the switch expression will be explored later in the section on pattern matching.


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