How to do it...

1. Create a new playground file in Xcode called Extensions.
2. Create extension for double value by adding computing properties, as follows:

      extension Double{ 
    
        var absoluteValue: Double{ 
          return abs(self) 
        } 
    
        var intValue: Int{ 
          return Int(self) 
        } 
      } 
 
      extension String{ 
    
        var length: Int{ 
          return self.characters.count 
        } 
      } 
 
      let doubleValue: Double = -19.5 
      doubleValue.absoluteValue // 19.5 
      doubleValue.intValue // 19 
 
      extension Int{ 
    
        func isEven() ->Bool{ 
          return self % 2 == 0 
        } 
    
        func isOdd() ->Bool{ 
          return !isEven() 
        } 
    
        func digits() -> [Int]{ 
          var digits = [Int]() 
          var num = self 
          repeat { 
            
            let digit = num % 10 
            digits.append(digit) 
            num /= 10 
            
          } while num != 0 
        
          return digits 
        } 
      } 
 
      let num = 12345 
      num.digits()  // [5, 4, 3, 2, 1]