11.3. Assertions

Assertions are not part of the interface to a routine. Rather, they are an internal consistency check within a piece of code, to ensure that the computation is proceeding as expected.

11.3.1. assert statements

assert statements specify a boolean expression that must evaluate to true; otherwise it is a fatal error.
private attr arr:ARRAY{INT};
sum_of_elts is
   sum:INT := 0;
   loop e ::= arr.elt!;
      assert e > 0;
      sum := sum + e;
   return sum;

In the above piece of code, we expect the class to only be storing postive values in the array 'arr' . To double check this, when adding the elements together, we check whether each element is positive.