SERVER-24508 DocumentComparator and ValueComparator

 - Changes the Document/Value library to require comparisons
   to be made in the context of a comparator object. This is
   prep work for full collation support in the aggregation
   system.
 - Adds injectExpressionContext() to propagate the
   ExpressionContext containing the comparator object to all
   DocumentSource, Accumulator, and Expression instances
   involved in the Pipeline.

1 files changed, 57 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/value_comparator.cpp b/src/mongo/db/pipeline/value_comparator.cpp
new file mode 100644
index 00000000000..a20a9460b6d
--- /dev/null
+++ b/src/mongo/db/pipeline/value_comparator.cpp
@@ -0,0 +1,57 @@
+/**
+ *    Copyright (C) 2016 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/pipeline/value_comparator.h"
+
+#include "mongo/util/assert_util.h"
+
+namespace mongo {
+
+bool ValueComparator::evaluate(Value::DeferredComparison deferredComparison) const {
+    int cmp = Value::compare(deferredComparison.lhs, deferredComparison.rhs, _stringComparator);
+    switch (deferredComparison.type) {
+        case Value::DeferredComparison::Type::kLT:
+            return cmp < 0;
+        case Value::DeferredComparison::Type::kLTE:
+            return cmp <= 0;
+        case Value::DeferredComparison::Type::kEQ:
+            return cmp == 0;
+        case Value::DeferredComparison::Type::kGTE:
+            return cmp >= 0;
+        case Value::DeferredComparison::Type::kGT:
+            return cmp > 0;
+        case Value::DeferredComparison::Type::kNE:
+            return cmp != 0;
+    }
+
+    MONGO_UNREACHABLE;
+}
+
+}  // namespace mongo