SERVER-30189 Reduce calls to allocator for large $in expressions

(cherry picked from commit 50a1afafc816097ed57804ff7033dffd85dbe160)

1 files changed, 11 insertions, 0 deletions

diff --git a/src/mongo/bson/bson_comparator_interface_base.h b/src/mongo/bson/bson_comparator_interface_base.h
index f70bec7b872..29d80916f72 100644
--- a/src/mongo/bson/bson_comparator_interface_base.h
+++ b/src/mongo/bson/bson_comparator_interface_base.h
@@ -28,9 +28,11 @@
 
 #pragma once
 
+#include <boost/container/flat_set.hpp>
 #include <initializer_list>
 #include <map>
 #include <set>
+#include <vector>
 
 #include "mongo/base/disallow_copying.h"
 #include "mongo/base/string_data_comparator_interface.h"
@@ -51,6 +53,9 @@ class BSONComparatorInterfaceBase {
     MONGO_DISALLOW_COPYING(BSONComparatorInterfaceBase);
 
 public:
+    BSONComparatorInterfaceBase(BSONComparatorInterfaceBase&& other) = default;
+    BSONComparatorInterfaceBase& operator=(BSONComparatorInterfaceBase&& other) = default;
+
     /**
      * A deferred comparison between two objects of type T, which can be converted into a boolean
      * via the evaluate() method.
@@ -122,6 +127,8 @@ public:
 
     using Set = std::set<T, LessThan>;
 
+    using FlatSet = boost::container::flat_set<T, LessThan>;
+
     using UnorderedSet = stdx::unordered_set<T, Hasher, EqualTo>;
 
     template <typename ValueType>
@@ -207,6 +214,10 @@ protected:
         return Set(init, LessThan(this));
     }
 
+    FlatSet makeFlatSet(const std::vector<T>& elements) const {
+        return FlatSet(elements.begin(), elements.end(), LessThan(this));
+    }
+
     UnorderedSet makeUnorderedSet(std::initializer_list<T> init = {}) const {
         return UnorderedSet(init, 0, Hasher(this), EqualTo(this));
     }