Ruby on Rails 3 : “superclass mismatch for class …”

Question

Platform: Mac OSX 10.6

In my terminal, i start the Ruby console with \"rails c\"

While following the Ruby on Rails 3 tutorial to build a class:

Answer 1

Sometimes we 'open class' without us knowing. For example with some deep module nesting:

# space_gun.rb
class SpaceGun << Weapon
  def fire
    Trigger.fire
  end
end

# space_gun/trigger.rb
class SpaceGun
  class Trigger
  end
end

When we define trigger, we open the existing SpaceGun class. This works. However if we load the two file in the reverse order, the error would be raised, because we would define a SpaceGun class first, but is not a Weapon.

Sometimes we make this mistake because we explicitly require sub module (e.g. trigger) from the parent class. Which means the class definition will be done the reverse order, causing this issue.

# surely nothing can go wrong if we require what we need first right?
require 'space_gun/trigger'
class SpaceGun << Weapon
  def fire
    Trigger.fire
  end
end
# BOOM

Either

1. rely on auto loading
2. always put inheritance to every open class occurrence.