34.6.3 Methods

All class methods must be defined within methods blocks. An exception to this rule is described at the end of this subsection. Those methods blocks can have additional attributes specifying the access rights or whether the methods are static, i.e., methods that can be called without creating an object of that class.

classdef some_class
  methods
    function obj = some_class ()
      disp ("New instance created.");
    endfunction

    function disp (obj)
      disp ("Here is some_class.");
    endfunction
  endmethods

  methods (Access = mode)
    function r = func (obj, r)
      r = 2 * r;
    endfunction
  endmethods

  methods (Static = true)
    function c = circumference (radius)
      c = 2 * pi () .* radius;
    endfunction
  endmethods
endclassdef

The constructor of the class is declared in the methods block and must have the same name as the class and exactly one output argument which is an object of its class.

It is also possible to overload built-in or inherited methods, like the disp function in the example above to tell Octave how objects of some_class should be displayed (see Class Methods).

In general, the first argument in a method definition is always the object that it is called from. Class methods can either be called by passing the object as the first argument to that method or by calling the object followed by a dot (".") and the method’s name with subsequent arguments:

>> obj = some_class ();
New instance created.
>> disp (obj);   # both are
>> obj.disp ();  # equal

In some_class, the method func is defined within a methods block setting the Access attribute to mode, which is one of:

public

The methods can be accessed from everywhere.

private

The methods can only be accessed from other class methods. Subclasses of that class cannot access them.

protected

The methods can only be accessed from other class methods and from subclasses of that class.

The default access for methods is public.

Finally, the method circumference is defined in a static methods block and can be used without creating an object of some_class. This is useful for methods, that do not depend on any class properties. The class name and the name of the static method, separated by a dot ("."), call this static method. In contrast to non-static methods, the object is not passed as first argument even if called using an object of some_class.

>> some_class.circumference (3)
⇒ ans =  18.850
>> obj = some_class ();
New instance created.
>> obj.circumference (3)
⇒ ans =  18.850

Additionally, class methods can be defined as functions in a folder of the same name as the class prepended with the ‘@’ symbol (see Creating a Class). The main classdef file has to be stored in this class folder as well.