1 files changed, 50 insertions, 0 deletions
diff --git a/mtraits/noconflict.py b/mtraits/noconflict.py
new file mode 100644
index 0000000..bbdb678
--- /dev/null
+++ b/mtraits/noconflict.py
@@ -0,0 +1,50 @@
+"""
+An helper module for meta-type conflict resolution
+"""
+
+import inspect, types
+
+memoized_metaclasses_map = {}
+
+def skip_redundant(iterable, skipset=None):
+   "Redundant items are repeated items or items in the original skipset."
+   if skipset is None: skipset = set()
+   for item in iterable:
+       if item not in skipset:
+           skipset.add(item)
+           yield item
+
+def remove_redundant(metaclasses):
+   skipset = set([types.ClassType])
+   for meta in metaclasses: # determines the metaclasses to be skipped
+       skipset.update(inspect.getmro(meta)[1:])
+   return tuple(skip_redundant(metaclasses, skipset))
+
+# make tuple of needed metaclasses in specified priority order
+def get_noconflict_metaclass(bases, left_metas, right_metas):
+    metas = left_metas + tuple(map(type, bases)) + right_metas
+    needed_metas = remove_redundant(metas)
+
+    # return existing confict-solving meta, if any
+    if needed_metas in memoized_metaclasses_map:
+        return memoized_metaclasses_map[needed_metas]
+    # nope: compute, memoize and return needed conflict-solving meta
+    elif not needed_metas: # wee, a trivial case, happy us
+        meta = type
+    elif len(needed_metas) == 1: # another trivial case
+        meta = needed_metas[0]
+    # check for recursion, can happen i.e. for Zope ExtensionClasses
+    elif needed_metas == bases: 
+        raise TypeError("Incompatible root metatypes", needed_metas)
+    else: # gotta work ...
+        metaname = '_' + ''.join(m.__name__ for m in needed_metas)
+        meta = classmaker()(metaname, needed_metas, {})
+    memoized_metaclasses_map[needed_metas] = meta
+    return meta
+
+# recursive builder used in conjunction with get_noconflict_metaclass
+def classmaker(left_metas=(), right_metas=()):
+    def make_class(name, bases, adict):
+        metaclass = get_noconflict_metaclass(bases, left_metas, right_metas)
+        return metaclass(name, bases, adict)
+    return make_class