Member visibility

Like formulas, class declarations are divided in three sections, called public, protected, and private (in this order). Each section can contain member declarations: fields and methods. The type of section determines the visibility of the members that it contains.

• Members in the public section are accessible to formulas and other classes. This is the public interface of the class: the part that is intended to be visible to the outside world.
• Members in the protected section are accessible only to derived classes. This is often useful to change the inherited behavior of a class in a descendant. See Inheritance.
• Members in the private section can only be accessed by methods from the same class. Formulas or other classes cannot access them. This is useful for storing the internal data for the class, because you are sure that no other class can interfere with it.

Generally, the public section contains the constructor for the class, and the methods that make up its public interface. All fields and internal methods should go into the private section. If it is necessary to access a field from outside the class, the best design is to create a method to access it (commonly called a getter or setter). This allows you to change the internal representation of the class later, while keeping the public interface the same.

If you do not specify a section, it is assumed to be public. Many examples in this help file use this for brevity, but for real classes, it is recommended to define the visibility explicitly.

Here is an example of a simple Texture class that can distort a complex value:

class Texture {
public:
  func Texture()
    fAmount = 0.1
    fSeed = 1234
  endfunc

  complex func distort(const complex x)
  ; Adds a small random value to x and returns the result.
    return real(x) + getRandomValue() + flip(imag(x) + getRandomValue())
  endfunc

  float func getAmount()
  ; Returns the amount of distortion.
    return fAmount
  endfunc
  
  func setAmount(const float amount)
  ; Sets the amount of distortion
    fAmount = amount
  endfunc
  
private:
  float fAmount
  int fSeed
  
  float func getRandomValue()
  ; Return a new random value using the current seed.
    fSeed = random(fSeed)
    return fAmount * (fSeed / #randomrange)
  endfunc
}

All fields in this class are private, and the amount of distortion can be accessed with getAmount and setAmount. The getRandomValue method is private because it is only used within the class.

For completeness, here is how you would use this class:

Texture tx = new Texture
print(tx.distort((2, 3)))  ; Prints (1.968, 2.945)
print(tx.distort((2, 3)))  ; Prints (2.001, 3.062)

Note: Classes can also have a default section for specifying the title and parameters of the class. See Plug-in parameters.

Next: Inheritance

See Also
Classes
Fields
Methods