Match

Match

We will skip this material on match statements if we don't have time. Please read it as the match statement can be pretty useful.

The match statement can be more efficient and easier to read if there is a multi-way conditional statement whose branches depend on the integer values of an expression. For example, recall the following from above:

   method onMousePress (point: Point) {

      nextLineStarts := point

      def colorNumber: Number = randomIntFrom(1) to (3)
      if (colorNumber == 1) then {
         lineColor := red
      } elseif (colorNumber == 2) then {
         lineColor := white
      } else {
         lineColor := blue
      }
   }

A match statement can choose the correct statements to execute based on the value of colorNumber (see program SpirographThreeColorMatch

      def colorNumber: Number = randomIntFrom (1) to (3)
      match(colorNumber) 
         case {1 -> lineColor := red}
         case {2 -> lineColor := white}
         case {3 -> lineColor := blue}

Note that each branch is executed when the value of randomIntFrom()to is an exact match for the number after case. It is possible to also write a default case to be executed if none of the others match. For example we could write

       case {_ -> print "no match -- this wasn't supposed to happen!!"}

In the above case, the underscore is a wildcard that matches everything.

Note that you cannot use inequalities or other boolean expressions in cases.

Match