From d59ff1d57f7bf152d055bb05eee20684e8e3c18d Mon Sep 17 00:00:00 2001
From: Kyle Suarez <kyle.suarez@mongodb.com>
Date: Fri, 21 Jul 2017 11:42:01 -0400
Subject: SERVER-30030 create an $_internalSchemaCond MatchExpression

---
 src/mongo/db/matcher/expression_arity.h | 140 ++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 src/mongo/db/matcher/expression_arity.h

(limited to 'src/mongo/db/matcher/expression_arity.h')

diff --git a/src/mongo/db/matcher/expression_arity.h b/src/mongo/db/matcher/expression_arity.h
new file mode 100644
index 00000000000..07196a56900
--- /dev/null
+++ b/src/mongo/db/matcher/expression_arity.h
@@ -0,0 +1,140 @@
+/**
+ * Copyright (C) 2017 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.
+ */
+
+#pragma once
+
+#include <algorithm>
+#include <array>
+
+#include "mongo/db/matcher/expression.h"
+#include "mongo/stdx/memory.h"
+
+namespace mongo {
+
+/**
+ * Abstract base class for MatchExpressions that take a fixed 'nargs' number of MatchExpression
+ * arguments. 'T' is the MatchExpression class that extends this interface.
+ */
+template <typename T, size_t nargs>
+class FixedArityMatchExpression : public MatchExpression {
+public:
+    /**
+     * The number of arguments accepted by this expression.
+     */
+    static constexpr size_t arity() {
+        return nargs;
+    }
+
+    virtual ~FixedArityMatchExpression() = default;
+
+    void debugString(StringBuilder& debug, int level) const final {
+        _debugAddSpace(debug, level);
+
+        BSONObjBuilder builder;
+        serialize(&builder);
+        debug << builder.obj().toString();
+    }
+
+    /**
+     * The order of arguments is significant when determining equivalence.
+     */
+    bool equivalent(const MatchExpression* expr) const final {
+        if (matchType() != expr->matchType()) {
+            return false;
+        }
+
+        auto other = static_cast<const T*>(expr);
+        const auto& ourChildren = _expressions;
+        const auto& theirChildren = other->_expressions;
+        return std::equal(
+            ourChildren.begin(),
+            ourChildren.end(),
+            theirChildren.begin(),
+            theirChildren.end(),
+            [](const auto& expr1, const auto& expr2) { return expr1->equivalent(expr2.get()); });
+    }
+
+    /**
+     * Takes ownership of the MatchExpressions in 'expressions'.
+     */
+    void init(std::array<std::unique_ptr<MatchExpression>, nargs> expressions) {
+        _expressions = std::move(expressions);
+    }
+
+    /**
+     * The name of this MatchExpression.
+     */
+    virtual StringData name() const = 0;
+
+    /**
+     * Serializes each subexpression sequentially in a BSONArray.
+     */
+    void serialize(BSONObjBuilder* builder) const final {
+        BSONArrayBuilder exprArray(builder->subarrayStart(name()));
+        for (const auto& expr : _expressions) {
+            BSONObjBuilder exprBuilder(exprArray.subobjStart());
+            expr->serialize(&exprBuilder);
+            exprBuilder.doneFast();
+        }
+        exprArray.doneFast();
+    }
+
+    /**
+     * Clones this MatchExpression by recursively cloning each sub-expression.
+     */
+    std::unique_ptr<MatchExpression> shallowClone() const final {
+        std::unique_ptr<T> clone = stdx::make_unique<T>();
+        std::array<std::unique_ptr<MatchExpression>, nargs> clonedExpressions;
+        std::transform(_expressions.begin(),
+                       _expressions.end(),
+                       clonedExpressions.begin(),
+                       [](const auto& orig) {
+                           return orig ? orig->shallowClone()
+                                       : std::unique_ptr<MatchExpression>(nullptr);
+                       });
+        clone->_expressions = std::move(clonedExpressions);
+
+        if (getTag()) {
+            clone->setTag(getTag()->clone());
+        }
+
+        return std::move(clone);
+    }
+
+protected:
+    explicit FixedArityMatchExpression(MatchType type) : MatchExpression(type) {}
+
+    const auto& expressions() const {
+        return _expressions;
+    }
+
+private:
+    std::array<std::unique_ptr<MatchExpression>, nargs> _expressions;
+};
+
+}  // namespace mongo
-- 
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