Creating a classdef Class (GNU Octave (version 6.2.0))

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#### 34.6.1 Creating a `classdef` Class

A very basic `classdef` value class (see Value Classes vs. Handle Classes) is defined by:

    classdef some_class
      properties
      endproperties

      methods
      endmethods
    endclassdef

In contrast to old style classes, the `properties`-`endproperties` block as well as the `methods`-`endmethods` block can be used to define properties and methods of the class. Because both blocks are empty, they can be omitted in this particular case.

For simplicity, a more advanced implementation of a `classdef` class is shown using the `polynomial` example again (see Creating a Class):

    classdef polynomial2
      properties
        poly = 0;
      endproperties

      methods
        function p = polynomial2 (a)
          if (nargin > 1)
            print_usage ();
          endif

          if (nargin == 1)
            if (isa (a, "polynomial2"))
              p.poly = a.poly;
            elseif (isreal (a) && isvector (a))
              p.poly = a(:).';  # force row vector
            else
              error ("polynomial2: A must be a real vector");
            endif
          endif
        endfunction

        function disp (p)
          a = p.poly;
          first = true;
          for i = 1 : length (a);
            if (a(i) != 0)
              if (first)
                first = false;
              elseif (a(i) > 0 || isnan (a(i)))
                printf (" +");
              endif
              if (a(i) < 0)
                printf (" -");
              endif
              if (i == 1)
                printf (" %.5g", abs (a(i)));
              elseif (abs (a(i)) != 1)
                printf (" %.5g *", abs (a(i)));
              endif
              if (i > 1)
                printf (" X");
              endif
              if (i > 2)
                printf (" ^ %d", i - 1);
              endif
            endif
          endfor

          if (first)
            printf (" 0");
          endif
          printf ("\n");
        endfunction
      endmethods
    endclassdef

An object of class `polynomial2` is created by calling the class constructor:

    >> p = polynomial2 ([1, 0, 1])
    ⇒ p =

     1 + X ^ 2