How it works...

In Double type, we have added two computed properties. The computed properties are properties that will be calculated every time when it's called. We've added a property called absoluteValue, which returns the absolute value; same for intValue, which returns the integer value of double. Then, for any double value in the whole project, these two properties are accessible and can be used.

In the Int type, we have defined three new instance methods. The isEven() method should return true if this number is even, false otherwise, and the same logic applies for isOdd(). The third method that has some more logic is digits(), which returns array of digits in the number. The algorithm is simple; we get the last digit by getting the remainder of piding the number by 10, and then skip the last digit by piding by 10.