# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@fb.com>
# Date 2014-10-03 00:22:17
# Node ID aeacc2055f0de57016b142aaa9ec451d2bcc7119
# Parent  f7b0ebe6ad422254b31d6b5ccb8c4c544e404334

abstractsmartset: add default implementation for __sub__

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2291,7 +2291,8 @@ class abstractsmartset(object):
         """Returns a new object with the substraction of the two collections.
 
         This is part of the mandatory API for smartset."""
-        raise NotImplementedError()
+        c = other.__contains__
+        return self.filter(lambda r: not c(r))
 
     def filter(self, condition):
         """Returns this smartset filtered by condition as a new smartset.