Problem creating get function for custom Octave object

gistfile1.matlab

## octave --version
## GNU Octave, version 3.6.1

## file: @triangle/triangle.m

function t = triangle (p1, p2, p3)

  if (nargin == 3)
    if (isvector(p1) && isreal(p1) && length(p1) == 3 &&
        isvector(p2) && isreal(p2) && length(p2) == 3 &&
        isvector(p3) && isreal(p3) && length(p3) == 3)

      t.p1 = p1;
      t.p2 = p2;
      t.p3 = p3;

      t = class(t, "triangle");

    else
      error("triangle: expecting real 3d vectors");
    endif
  else
    print_usage();
  endif

endfunction


## file: @triangle/get.m


function s = get (t, f)
  if (nargin == 1)
    s.p1 = t.p1;
    s.p2 = t.p2;
    s.p3 = t.p3;
  elseif (nargin == 2)
    if (ischar (f))
      switch (f)
        case "points"
          s = [t.p1 t.p2 t.p3];
        otherwise
          error ("get: invalid property %s", f);
      endswitch
    else
      error ("get: expecting the property to be a string");
    endif
  else
    print_usage ();
  endif
endfunction


# octave interpreter:

addpath("/path/to/folder/containing@triangle")

t = triangle([0 0 0],[1 0 0],[1 1 0])
t = <class triangle>

get(t)
error: octave_base_value::array_value(): wrong type argument `class'
error: get: expecting graphics handle as first argument