Inheritence as explained in the Design Document does not work

[pieterproigia]

Inheritence as described in http://tw2core.readthedocs.org/en/latest/design/#declarative-instantiation does not work. Example code:

import tw2.core as twc
import tw2.devtools
import tw2.forms as twf

class Index(twf.FormPage):
    class MyFields(twc.CompoundWidget):
        b = twf.TextArea()
        x = twf.Label(text='this is a test')
        c = twf.TextField()

    class TableFields(MyFields, twf.TableLayout):
        pass

    class ListFields(MyFields, twf.ListLayout):
        b = twf.TextField()

tw2.devtools.dev_server()

Gives the following error:

Traceback (most recent call last):
  File "myapp.py", line 5, in <module>
    class Index(twf.FormPage):
  File "myapp.py", line 15, in Index
    class ListFields(MyFields, twf.ListLayout):
  File "/home/pieter/.virtualenvs/tw2dev/local/lib/python2.7/site-packages/tw2/core/widgets.py", line 81, in __new__
    w.post_define.__func__(widget)
  File "/home/pieter/.virtualenvs/tw2dev/local/lib/python2.7/site-packages/tw2/core/widgets.py", line 604, in post_define
    raise core.WidgetError("Duplicate id '%s'" % c.id)
tw2.core.core.WidgetError: Duplicate id 'b'