Take a look on the snippet below

  # points is an array of structure-objects defining a point
  points[0].x = 5
  points[0].y = 4
  1.upto(points.length) { |i|
    points[i].x = points[i-1].x
    points[i].y = points[i-1].y
  }

Now that looks like a legal bunch of statements, right? The thing is
every time Ruby interpret the line 'points[i].x = points[i-1].x' it
stops, giving me nothing but a cryptic error message, 'undefined
method `x=' for nil (NameError)'.
Could someone please tell me what's going on?

-johan