diff --git a/tdutils/CMakeLists.txt b/tdutils/CMakeLists.txt
index 9a04afcb..52d2dcac 100644
--- a/tdutils/CMakeLists.txt
+++ b/tdutils/CMakeLists.txt
@@ -190,6 +190,7 @@ set(TDUTILS_SOURCE
 
 set(TDUTILS_TEST_SOURCE
   ${CMAKE_CURRENT_SOURCE_DIR}/test/crypto.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/test/Enumerator.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/test/filesystem.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/test/gzip.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/test/HazardPointers.cpp
diff --git a/tdutils/td/utils/Enumerator.h b/tdutils/td/utils/Enumerator.h
new file mode 100644
index 00000000..a38fc542
--- /dev/null
+++ b/tdutils/td/utils/Enumerator.h
@@ -0,0 +1,86 @@
+//
+// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+#pragma once
+#include "td/utils/common.h"
+#include "td/utils/misc.h"
+
+#include <set>
+
+namespace td {
+
+template <class ValueT>
+class Enumerator {
+ public:
+  using Key = int32;
+  template <class T>
+  Key add(T &&value) {
+    ValueT v = std::forward<T>(value);
+    container_->set_zero_value(&v);
+    auto it = set_.lower_bound(Key{0});
+    container_->set_zero_value(nullptr);
+    if (it != set_.end() && container_->get_value(*it) == v) {
+      return *it;
+    }
+    auto key = container_->add_value(std::move(v));
+    set_.insert(it, key);
+    return key;
+  }
+  ValueT &get(Key key) {
+    return container_->get_value(key);
+  }
+  const ValueT &get(Key key) const {
+    return container_->get_value(key);
+  }
+
+ private:
+  class Container {
+   public:
+    bool compare(Key a, Key b) const {
+      return get_value(a) < get_value(b);
+    }
+    const ValueT &get_value(Key key) const {
+      if (key == 0) {
+        CHECK(zero_value_);
+        return *zero_value_;
+      }
+      size_t pos = narrow_cast<size_t>(key - 1);
+      CHECK(pos < values_.size());
+      return values_[pos];
+    }
+    ValueT &get_value(Key key) {
+      return const_cast<ValueT &>(const_cast<const Container *>(this)->get_value(key));
+    }
+    void set_zero_value(ValueT *value) {
+      zero_value_ = value;
+    }
+    Key add_value(ValueT &&value) {
+      values_.push_back(std::move(value));
+      return narrow_cast<Key>(values_.size());
+    }
+
+   private:
+    std::vector<ValueT> values_;
+    ValueT *zero_value_ = nullptr;
+  };
+
+  class Comparator {
+   public:
+    explicit Comparator(Container *container) : container_(container) {
+    }
+    bool operator()(Key a, Key b) const {
+      return container_->compare(a, b);
+    }
+
+   private:
+    Container *container_;
+  };
+
+  std::unique_ptr<Container> container_{std::make_unique<Container>()};
+  std::set<Key, Comparator> set_{Comparator{container_.get()}};
+};
+
+}  // namespace td
diff --git a/tdutils/test/Enumerator.cpp b/tdutils/test/Enumerator.cpp
new file mode 100644
index 00000000..e087fe22
--- /dev/null
+++ b/tdutils/test/Enumerator.cpp
@@ -0,0 +1,27 @@
+//
+// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+#include "td/utils/Enumerator.h"
+#include "td/utils/logging.h"
+#include "td/utils/port/thread.h"
+#include "td/utils/Random.h"
+#include "td/utils/tests.h"
+
+TEST(Enumerator, simple) {
+  td::Enumerator<std::string> e;
+  auto b = e.add("b");
+  auto a = e.add("a");
+  auto d = e.add("d");
+  auto c = e.add("c");
+  ASSERT_STREQ(e.get(a), "a");
+  ASSERT_STREQ(e.get(b), "b");
+  ASSERT_STREQ(e.get(c), "c");
+  ASSERT_STREQ(e.get(d), "d");
+  ASSERT_EQ(a, e.add("a"));
+  ASSERT_EQ(b, e.add("b"));
+  ASSERT_EQ(c, e.add("c"));
+  ASSERT_EQ(d, e.add("d"));
+}