1 files changed, 27 insertions, 0 deletions
diff --git a/lib/rubygems/resolver/set.rb b/lib/rubygems/resolver/set.rb
new file mode 100644
index 0000000000..32c137ef6b
--- /dev/null
+++ b/lib/rubygems/resolver/set.rb
@@ -0,0 +1,27 @@
+##
+# Resolver sets are used to look up specifications (and their
+# dependencies) used in resolution.  This set is abstract.
+
+class Gem::Resolver::Set
+
+  ##
+  # The find_all method must be implemented.  It returns all Resolver
+  # Specification objects matching the given DependencyRequest +req+.
+
+  def find_all req
+    raise NotImplementedError
+  end
+
+  ##
+  # The #prefetch method may be overridden, but this is not necessary.  This
+  # default implementation does nothing, which is suitable for sets where
+  # looking up a specification is cheap (such as installed gems).
+  #
+  # When overridden, the #prefetch method should look up specifications
+  # matching +reqs+.
+
+  def prefetch reqs
+  end
+
+end
+