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..970d8a9c1c55e733e331fa58228c66699ea64da2
--- /dev/null
+++ b/impl/memory/stringset.go
@@ -0,0 +1,19 @@
+// 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) Add(value string) {

[dnj, 2015/08/28 20:15:04]

nit: Methods should not be exported, since stringSet is not exported.

nit: IMO would increase value of this if you added a "func (...) contains(value
string) {...}

Then logic using it would look like:
if !sset.contains("myvalue") {
  // do stuff
  sset.add("myvalue")
}

etc., which reads cleaner than:
if _, ok := sset["myvalue"]; ok {
  // do stuff
  sset["myvalue"] = struct{}{}
}

[iannucci, 2015/08/28 20:38:50]

done. though I usually prefer to export them like this when it seems likely that
the type could conceivably be in a different package and is prone to be lifted
later.
Done and added some other goodies.

+	s[value] = struct{}{}
+}
+
+func (s stringSet) Dup() stringSet {
+	ret := make(stringSet, len(s))
+	for v := range s {
+		ret.Add(v)
+	}
+	return ret
+}