Classes

While function declarations in formulas are useful, you cannot access them from another formula. To be able to re-use code in multiple formulas, you need to use classes instead.

• A class is a declaration of a set of variables and functions that operate on these variables.
• An object is an instance of its class. This class is the type of the object, just like int is the type of an integer variable.
• The variables of a class are called fields.
• The functions of a class are called methods. Both fields and methods are also known as the members of a class.

Classes are declared in formula files, or in plug-in library files with the .ulb file extension. A class looks a bit like a regular formula entry, but the entry identifier is preceded by the class keyword. Here is an example of a simple class that represents a point with integer coordinates:

class Point {
public:
  func Point(int aX, int aY)
    x = aX
    y = aY
  endfunc

  float func distance(Point p)
  ; Returns the distance to the second point p.
    return sqrt(sqr(p.x - x) + sqr(p.y - y))
  endfunc

  int x
  int y
} 

This class, named Point, contains a constructor, which is a special function that initializes an instance of the class. The constructor always has the same name as the class. Also, there is an additional method called distance, and two fields called x and y that store the coordinates of the point.

Next: Objects

See Also
Inheritance
Plug-in parameters