impl/memory: Implement Queries

impl/memory/stringset.go

Index: impl/memory/stringset.go
diff --git a/impl/memory/stringset.go b/impl/memory/stringset.go
new file mode 100644
index 0000000000000000000000000000000000000000..d803cb1bd065eb85c26f5050653c073b6e2d3505
--- /dev/null
+++ b/impl/memory/stringset.go
@@ -0,0 +1,39 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package memory
+
+type stringSet map[string]struct{}
+
+func (s stringSet) has(value string) bool {
+	_, ret := s[value]
+	return ret
+}
+
+// add adds to the set and returns true iff the value was not there before (i.e.
+// it returns true if add actually modifies the stringSet).
+func (s stringSet) add(value string) bool {
+	ret := !s.has(value)
+	s[value] = struct{}{}
+	return ret
+}
+
+func (s stringSet) rm(value string) {
+	delete(s, value)
+}
+
+func (s stringSet) dup() stringSet {
+	ret := make(stringSet, len(s))
+	for v := range s {
+		ret.add(v)
+	}
+	return ret
+}
+
+func (s stringSet) getOne() string {
+	for k := range s {
+		return k
+	}
+	return ""
+}