First implementation of flat sets

base/containers/flat_set_unittest.cc

Index: base/containers/flat_set_unittest.cc
diff --git a/base/containers/flat_set_unittest.cc b/base/containers/flat_set_unittest.cc
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index 0000000000000000000000000000000000000000..8d2ad1b28b257c25a285b15b2de43741399335c1
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+++ b/base/containers/flat_set_unittest.cc
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+// Copyright 2016 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.
+
+#include "base/containers/flat_set.h"
+
+// Following tests are ported and extended tests from libcpp for std::set.
+// They can be found here:
+// https://github.com/llvm-mirror/libcxx/tree/master/test/std/containers/associative/set
+//
+// Not ported tests:
+// * No tests with PrivateConstructor and std::less<> changed to std::less<T>
+//   These tests have to do with C++14 std::less<>
+//   http://en.cppreference.com/w/cpp/utility/functional/less_void
+//   and add support for templated versions of lookup functions.
+//   Current implementation of flat containers doesn't support it.
+// * No tests with TemplateConstructor.
+//   Library working group issue: LWG #2059
+//   http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2059
+//   There is an ambiguity between erase with an iterator and erase with a key,
+//   if key has a templated constructor. We have to fix this.
+// * No tests for max_size()
+//   Has to do with allocator support.
+// * No tests with DefaultOnly.
+//   Standard containers allocate each element in the separate node on the heap
+//   and then manipulate these nodes. Flat containers store their elements in
+//   contiguous memory and move them around, type is required to be movable.
+// * No tests for N3644.
+//   This proposal suggests that all default constructed iterators compare
+//   equal. Currently we use std::vector iterators and they don't implement
+//   this.
+// * No tests with min_allocator.
+//   Allocators are not widely used in Chromium, and how we are going to
+//   customize underlying data (if we are going to) is still up to debate.
+// * No tests counting allocations. Flat sets have different allocation
+//   patterns than std::sets and we do not consider them to be a part of the
+//   interface.
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+class MoveOnly {
+ public:
+  MoveOnly(int data = 1) : data_(data) {}
+  MoveOnly(MoveOnly&& x) : data_(x.data_) { x.data_ = 0; }
+  MoveOnly& operator=(MoveOnly&& x) {
+    data_ = x.data_;
+    x.data_ = 0;
+    return *this;
+  }
+
+  friend bool operator==(const MoveOnly& x, const MoveOnly& y) {

[Peter Kasting, 2016/12/20 02:33:51]

Any particular reason to prefer member vs. non-member for these relational
operators?

[dyaroshev, 2016/12/20 21:59:55]

1. This type is implicitly convertible from int (to make tests more readable)
and this allows me to do 1 == MoveOnly(1) as well as MoveOnly(1) == 1. So for
example EXPECT_EQ(1, MoveOnly(1)); will work.
2. This is generally considered to be the preferable way, because there is no
semantic difference between left and right operand, while member form implies
one.

+    return x.data_ == y.data_;
+  }
+
+  friend bool operator<(const MoveOnly& x, const MoveOnly& y) {
+    return x.data_ < y.data_;
+  }
+
+  int data() const { return data_; }
+
+ private:
+  int data_;
+
+  DISALLOW_COPY_AND_ASSIGN(MoveOnly);
+};
+
+template <class It>
+class InputIterator {
+ public:
+  using iterator_category = std::input_iterator_tag;
+  using value_type = typename std::iterator_traits<It>::value_type;
+  using difference_type = typename std::iterator_traits<It>::difference_type;
+  using pointer = It;
+  using reference = typename std::iterator_traits<It>::reference;
+
+  InputIterator() : it_() {}
+  explicit InputIterator(It it) : it_(it) {}
+  InputIterator(const InputIterator& x) : it_(x.it_) {}
+
+  reference operator*() const { return *it_; }
+  pointer operator->() const { return it_; }
+
+  InputIterator& operator++() {
+    ++it_;
+    return *this;
+  }
+  InputIterator operator++(int) {
+    InputIterator tmp(*this);
+    ++(*this);
+    return tmp;
+  }
+
+  friend bool operator==(const InputIterator& x, const InputIterator& y) {
+    return x.it_ == y.it_;
+  }
+  friend bool operator!=(const InputIterator& x, const InputIterator& y) {
+    return !(x == y);
+  }
+
+ private:
+  It it_;
+};
+
+template <typename It>
+InputIterator<It> MakeInputIterator(It it) {
+  return InputIterator<It>(it);
+}
+
+class Emplaceable {
+ public:
+  Emplaceable() = default;
+  Emplaceable(int i, double d) : int_(i), double_(d) {}
+  Emplaceable(Emplaceable&& x) : int_(x.int_), double_(x.double_) {
+    x.int_ = 0;
+    x.double_ = 0.0;
+  }
+
+  Emplaceable& operator=(Emplaceable&& x) {
+    int_ = x.int_;
+    x.int_ = 0;
+    double_ = x.double_;
+    x.double_ = 0.0;
+    return *this;
+  }
+
+  friend bool operator==(const Emplaceable& x, const Emplaceable& y) {
+    return x.int_ == y.int_ && x.double_ == y.double_;
+  }
+
+  friend bool operator<(const Emplaceable& x, const Emplaceable& y) {
+    return std::tie(x.int_, x.double_) < std::tie(y.int_, y.double_);
+  }
+
+ private:
+  int int_ = 0;
+  double double_ = 0.0;

[Peter Kasting, 2016/12/20 02:33:51]

Nit: I dunno that I'm as big a fan of these initializers when we don't actually
use them except in one constructor.

Might be better to instead remove these and declare the first constructor as:

  Emplaceable() : Emplaceable(0, 0.0) {}

[dyaroshev, 2016/12/20 21:59:55]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(Emplaceable);
+};
+
+class NonDefaultConstructibleCompare {
+ public:
+  NonDefaultConstructibleCompare(int) {}
+
+  template <typename T>
+  bool operator()(const T& lhs, const T& rhs) {
+    return std::less<T>()(lhs, rhs);
+  }
+};
+
+template <typename T>
+std::string ToString(const T& val) {
+  return std::to_string(val);
+}
+
+std::string ToString(const MoveOnly& val) {
+  return std::to_string(val.data());
+}
+
+template <typename XRange, typename YRange>
+// Requires:
+//      XRange is ForwardRange
+//      YRange is ForwardRange
+//      ValueType<XRange> is EqualityComparable to ValueType<YRange>
+bool EqualRange(const XRange& x_range, const YRange& y_range) {
+  if (std::distance(x_range.begin(), x_range.end()) !=
+      std::distance(y_range.begin(), y_range.end()))
+    return false;
+
+  return std::equal(x_range.begin(), x_range.end(), y_range.begin());

[Peter Kasting, 2016/12/20 02:33:50]

Nit: Or just:

  return (std::distance(x_range.begin(), x_range.end()) ==
          std::distance(y_range.begin(), y_range.end())) &&
         std::equal(x_range.begin(), x_range.end(), y_range.begin());

[dyaroshev, 2016/12/20 21:59:55]

Done.

+}
+
+template <typename Range>
+// Requires:
+//      Range is InputRange
+//      ValueType<Range> is ConvertibleToString.
+std::string RangeToString(const Range& range) {
+  std::string res = "[";
+  for (const auto& val : range) {

[Peter Kasting, 2016/12/20 02:33:51]

Nit: {} unnecessary

[dyaroshev, 2016/12/20 21:59:55]

Done.

+    res += ToString(val) + ", ";
+  }
+  res += ']';
+  return res;
+}
+
+template <typename TestedRange>
+// Requires:
+//      TestedRange is ForwardRange
+//      ExpectedRange is ForwardRange
+//      ValueType<TestedRange> is EqualityComparable to int
+//      ValueType<TestedRange> is ConvertibleToString.
+void ExpectRange(const TestedRange& tested_range,
+                 const std::vector<int>& expected_range) {
+  EXPECT_TRUE(EqualRange(tested_range, expected_range))
+      << "Expected: " << RangeToString(expected_range)
+      << " Actual: " << RangeToString(tested_range);

[Peter Kasting, 2016/12/20 02:33:51]

Nit: Maybe put a comma at the beginning of this second string constant

[dyaroshev, 2016/12/20 21:59:55]

Done.

+}
+
+}  // namespace
+
+// ----------------------------------------------------------------------------
+// Class.
+
+// Check that base::flat_set and its iterators can be instantiated with an
+// incomplete type.
+
+TEST(FlatSet, IncompleteType) {
+  struct A {
+    using Set = base::flat_set<A>;
+    int data;
+    Set m;
+    Set::iterator it;
+    Set::const_iterator cit;
+
+    // We do not declare operator< because clang complains that it's unused.
+  };
+
+  A a;
+}
+
+TEST(FlatSet, Stability) {
+  using Pair = std::pair<int, int>;
+
+  struct LessByFirst {
+    bool operator()(const Pair& x, const Pair& y) { return x.first < y.first; }
+  };
+
+  using Set = base::flat_set<Pair, LessByFirst>;
+
+  auto AllSecondAreZero = [](const Set& cont) {
+    return std::all_of(cont.begin(), cont.end(),
+                       [](const Pair& elem) { return elem.second == 0; });
+  };
+
+  Set cont{{0, 0}, {1, 0}, {0, 1}, {2, 0}, {0, 2}, {1, 1}};
+  EXPECT_TRUE(AllSecondAreZero(cont)) << "initializer_list constructor";
+
+  cont.insert(Pair(0, 1));
+  EXPECT_TRUE(AllSecondAreZero(cont)) << "single insert";
+
+  cont.insert({{3, 0}, {0, 1}, {1, 1}, {3, 1}, {2, 1}, {3, 2}});
+  EXPECT_TRUE(AllSecondAreZero(cont)) << "initializer_list insert";
+}
+
+// ----------------------------------------------------------------------------
+// Types.
+
+// key_type
+// key_compare
+// value_type
+// value_compare
+// allocator_type
+// pointer
+// const_pointer
+// reference
+// const_reference
+// size_type
+// difference_type
+// iterator
+// const_iterator
+// reverse_iterator
+// const_reverse_iterator
+
+TEST(FlatSet, Types) {
+  using Set = base::flat_set<int>;
+
+  // These are guarantied to be portable.

[Peter Kasting, 2016/12/20 02:33:51]

Nit: guaranteed

[dyaroshev, 2016/12/20 21:59:55]

Done.

+  static_assert((std::is_same<int, Set::key_type>::value), "");
+  static_assert((std::is_same<int, Set::value_type>::value), "");
+  static_assert((std::is_same<std::less<int>, Set::key_compare>::value), "");
+  static_assert((std::is_same<std::less<int>, Set::value_compare>::value), "");
+  static_assert((std::is_same<int&, Set::reference>::value), "");
+  static_assert((std::is_same<const int&, Set::const_reference>::value), "");
+  static_assert((std::is_same<int*, Set::pointer>::value), "");
+  static_assert((std::is_same<const int*, Set::const_pointer>::value), "");
+}
+
+// ----------------------------------------------------------------------------
+// Lifetime.
+
+// flat_set()
+// flat_set(const Compare& comp, const Allocator& alloc = Allocator())
+// flat_set(const Allocator& alloc)
+
+TEST(FlatSet, DefaultConstructor) {
+  {
+    using Set = base::flat_set<int>;

[Peter Kasting, 2016/12/20 02:33:50]

This alias appears in basically every test.  Maybe define it at file scope and
only override it locally where needed.

[dyaroshev, 2016/12/20 21:59:55]

Moved all common typedefs in anonymous namespace. Done.

+
+    Set cont;
+    ExpectRange(cont, {});
+  }
+
+  {
+    using Set = base::flat_set<int, NonDefaultConstructibleCompare>;
+
+    Set cont{NonDefaultConstructibleCompare(0)};

[Peter Kasting, 2016/12/20 02:33:51]

Do you really need to use {} here?  (Maybe it avoids Most Vexing Parse?)

[dyaroshev, 2016/12/20 21:59:55]

Done.

+    ExpectRange(cont, {});
+  }
+}
+
+// flat_set(InputIterator first,
+//          InputIterator last,
+//          const Compare& comp = Compare(),
+//          const Allocator& alloc = Allocator())
+// flat_set(InputIterator first, InputIterator last, const Allocator& alloc)
+
+TEST(FlatSet, RangeConstructor) {
+  {
+    using Set = base::flat_set<int>;
+
+    Set::value_type ar[] = {1, 1, 1, 2, 2, 2, 3, 3, 3};
+
+    Set cont(MakeInputIterator(std::begin(ar)),
+             MakeInputIterator(std::end(ar)));
+    ExpectRange(cont, {1, 2, 3});
+  }
+  {
+    using Set = base::flat_set<int, NonDefaultConstructibleCompare>;
+
+    Set::value_type ar[] = {1, 1, 1, 2, 2, 2, 3, 3, 3};
+
+    Set cont(MakeInputIterator(std::begin(ar)), MakeInputIterator(std::end(ar)),
+             NonDefaultConstructibleCompare(0));
+    ExpectRange(cont, {1, 2, 3});
+  }
+}
+
+// flat_set(const flat_set& x)
+// flat_set(const flat_set& x, const Allocator& alloc)
+
+TEST(FlatSet, CopyConstructor) {
+  using Set = base::flat_set<int>;
+
+  Set original{1, 2, 3, 4};
+  Set copied(original);
+
+  ExpectRange(copied, {1, 2, 3, 4});
+  ExpectRange(original, {1, 2, 3, 4});
+  EXPECT_EQ(original, copied);
+}
+
+// flat_set(flat_set&& x)
+// flat_set(flat_set&& x, const Allocator& alloc)
+
+TEST(FlatSet, MoveConstructor) {
+  using Set = base::flat_set<MoveOnly>;
+
+  int input_range[] = {1, 2, 3, 4};
+
+  Set original(std::begin(input_range), std::end(input_range));
+  Set moved(std::move(original));
+
+  ExpectRange(moved, {1, 2, 3, 4});
+}
+
+//  flat_set(std::initializer_list<value_type> il,
+//           const Compare& comp = Compare(),
+//           const Allocator& alloc = Allocator())
+//  flat_set(std::initializer_list<value_type> il, const Allocator& a)
+
+TEST(FlatSet, InitializerListConstructor) {
+  {
+    using Set = base::flat_set<int>;
+
+    Set cont{1, 2, 3, 4, 5, 6, 10, 8};
+    ExpectRange(cont, {1, 2, 3, 4, 5, 6, 8, 10});
+  }
+  {
+    using Set = base::flat_set<int, NonDefaultConstructibleCompare>;
+
+    Set cont({1, 2, 3, 4, 5, 6, 10, 8}, NonDefaultConstructibleCompare(0));
+    ExpectRange(cont, {1, 2, 3, 4, 5, 6, 8, 10});
+  }
+}
+
+// ----------------------------------------------------------------------------
+// Assignments.
+
+// flat_set& operator=(const flat_set& x)
+
+TEST(FlatSet, CopyAssignable) {
+  using Set = base::flat_set<int>;
+
+  Set original{1, 2, 3, 4};
+  Set copied;
+  copied = original;
+
+  ExpectRange(copied, {1, 2, 3, 4});
+  ExpectRange(original, {1, 2, 3, 4});
+  EXPECT_EQ(original, copied);
+}
+
+// flat_set& operator=(flat_set&& x)
+
+TEST(FlatSet, MoveAssignable) {
+  using Set = base::flat_set<MoveOnly>;
+
+  int input_range[] = {1, 2, 3, 4};
+
+  Set original(std::begin(input_range), std::end(input_range));
+  Set moved;
+  moved = std::move(original);
+
+  ExpectRange(moved, {1, 2, 3, 4});
+}
+
+// flat_set& operator=(std::initializer_list<value_type> il)
+
+TEST(FlatSet, InitializerListAssignable) {
+  using Set = base::flat_set<int>;
+
+  Set cont{0};
+  cont = {1, 2, 3, 4, 5, 6, 10, 8};
+
+  EXPECT_EQ(static_cast<Set::size_type>(0), cont.count(0));

[Peter Kasting, 2016/12/20 02:33:51]

Nit: I still suggest using "0U" and similar for cases like this, as we do in all
our other tests.

[dyaroshev, 2016/12/20 21:59:55]

Done.

+  ExpectRange(cont, {1, 2, 3, 4, 5, 6, 8, 10});
+}
+
+// --------------------------------------------------------------------------
+// Memory management.
+
+// void reserve(size_type size)
+
+TEST(FlatSet, Reserve) {
+  using Set = base::flat_set<int>;
+  Set cont{1, 2, 3};
+
+  cont.reserve(5);
+  EXPECT_LE(static_cast<Set::size_type>(5), cont.capacity());
+}
+
+// size_type capacity() const
+
+TEST(FlatSet, Capacity) {
+  using Set = base::flat_set<int>;
+  Set cont{1, 2, 3};
+  EXPECT_LE(cont.size(), cont.capacity());
+  cont.reserve(5);
+  EXPECT_LE(cont.size(), cont.capacity());
+}
+
+// void shrink_to_fit()
+
+TEST(FlatSet, ShrinkToFit) {
+  using Set = base::flat_set<int>;
+  Set cont{1, 2, 3};
+
+  Set::size_type capacity_before = cont.capacity();
+  cont.shrink_to_fit();
+  EXPECT_GE(capacity_before, cont.capacity());
+}
+
+// ----------------------------------------------------------------------------
+// Size management.
+
+// void clear();
+
+TEST(FlatSet, Clear) {
+  using Set = base::flat_set<int>;
+
+  Set cont{1, 2, 3, 4, 5, 6, 7, 8};
+  cont.clear();
+  ExpectRange(cont, {});
+}
+
+// size_type size() const;
+
+TEST(FlatSet, Size) {
+  using Set = base::flat_set<int>;
+  Set cont;
+  EXPECT_EQ(static_cast<Set::size_type>(0), cont.size());
+  cont.insert(2);
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  cont.insert(1);
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  cont.insert(3);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  cont.erase(cont.begin());
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  cont.erase(cont.begin());
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  cont.erase(cont.begin());
+  EXPECT_EQ(static_cast<Set::size_type>(0), cont.size());
+}
+
+// bool empty() const;
+
+TEST(FlatSet, Empty) {
+  using Set = base::flat_set<int>;
+  Set cont;
+  EXPECT_TRUE(cont.empty());
+  cont.insert(1);
+  EXPECT_FALSE(cont.empty());
+  cont.clear();
+  EXPECT_TRUE(cont.empty());
+}
+
+// ----------------------------------------------------------------------------
+// Iterators.
+
+//       iterator begin();
+// const_iterator begin() const;
+//       iterator end();
+// const_iterator end()   const;
+//
+//       reverse_iterator rbegin();
+// const_reverse_iterator rbegin() const;
+//       reverse_iterator rend();
+// const_reverse_iterator rend()   const;
+//
+// const_iterator         cbegin()  const;
+// const_iterator         cend()    const;
+// const_reverse_iterator crbegin() const;
+// const_reverse_iterator crend()   const;
+
+TEST(FlatSet, Iterators) {
+  using Set = base::flat_set<int>;
+
+  Set cont{1, 2, 3, 4, 5, 6, 7, 8};
+
+  auto size = static_cast<Set::difference_type>(cont.size());
+
+  EXPECT_EQ(size, std::distance(cont.begin(), cont.end()));
+  EXPECT_EQ(size, std::distance(cont.cbegin(), cont.cend()));
+  EXPECT_EQ(size, std::distance(cont.rbegin(), cont.rend()));
+  EXPECT_EQ(size, std::distance(cont.crbegin(), cont.crend()));
+
+  {
+    Set::iterator it = cont.begin();
+    Set::const_iterator c_it = cont.cbegin();
+    EXPECT_EQ(it, c_it);
+    for (int j = 1; it != cont.end(); ++it, ++c_it, ++j) {
+      EXPECT_EQ(j, *it);
+      EXPECT_EQ(j, *c_it);
+    }
+  }
+  {
+    Set::reverse_iterator rit = cont.rbegin();
+    Set::const_reverse_iterator c_rit = cont.crbegin();
+    EXPECT_EQ(rit, c_rit);
+    for (int j = static_cast<int>(size); rit != cont.rend();
+         ++rit, ++c_rit, --j) {
+      EXPECT_EQ(j, *rit);
+      EXPECT_EQ(j, *c_rit);
+    }
+  }
+}
+
+// ----------------------------------------------------------------------------
+// Insert operations.
+
+// pair<iterator, bool> insert(const value_type& v);
+
+TEST(FlatSet, InsertCV) {
+  using Set = base::flat_set<int>;
+
+  Set cont;
+  int value = 2;

[Peter Kasting, 2016/12/20 02:33:51]

Does this test not test the same thing if you inline these values into the
insert() calls instead of storing in a temp?

[dyaroshev, 2016/12/20 21:59:55]

I was trying to make emphasise that it calls insert(const value_type&) not
insert(value_type&&).

[Peter Kasting, 2016/12/20 22:06:38]

Yeah, that's a good point.

+  std::pair<Set::iterator, bool> result = cont.insert(value);
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(cont.begin(), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  EXPECT_EQ(2, *result.first);
+
+  value = 1;
+  result = cont.insert(value);
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(cont.begin(), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  EXPECT_EQ(1, *result.first);
+
+  value = 3;
+  result = cont.insert(value);
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(std::prev(cont.end()), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result.first);
+
+  value = 3;
+  result = cont.insert(value);
+  EXPECT_FALSE(result.second);
+  EXPECT_EQ(std::prev(cont.end()), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result.first);
+}
+
+// pair<iterator, bool> insert(value_type&& v);
+
+TEST(FlatSet, InsertRV) {
+  using Set = base::flat_set<MoveOnly>;
+
+  Set cont;
+  std::pair<Set::iterator, bool> result = cont.insert(MoveOnly(2));
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(cont.begin(), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  EXPECT_EQ(2, *result.first);
+
+  result = cont.insert(MoveOnly(1));
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(cont.begin(), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  EXPECT_EQ(1, *result.first);
+
+  result = cont.insert(MoveOnly(3));
+  EXPECT_TRUE(result.second);
+  EXPECT_EQ(std::prev(cont.end()), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result.first);
+
+  result = cont.insert(MoveOnly(3));
+  EXPECT_FALSE(result.second);
+  EXPECT_EQ(std::prev(cont.end()), result.first);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(static_cast<Set::size_type>(3), *result.first);

[Peter Kasting, 2016/12/20 02:33:51]

This cast seems incorrect.

[dyaroshev, 2016/12/20 21:59:55]

Done.

+}
+
+// iterator insert(const_iterator position, const value_type& v);
+
+TEST(FlatSet, InsertIterCV) {
+  using Set = base::flat_set<int>;
+
+  Set cont;
+  Set::iterator result = cont.insert(cont.cend(), 2);
+  EXPECT_EQ(cont.begin(), result);
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  EXPECT_EQ(2, *result);
+
+  result = cont.insert(cont.cend(), 1);
+  EXPECT_EQ(cont.begin(), result);
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  EXPECT_EQ(1, *result);
+
+  result = cont.insert(cont.cend(), 3);
+  EXPECT_EQ(std::prev(cont.end()), result);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result);
+
+  result = cont.insert(cont.cend(), 3);
+  EXPECT_EQ(std::prev(cont.end()), result);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result);
+}
+
+// iterator insert(const_iterator position, value_type&& v);
+
+TEST(FlatSet, InsertIterRV) {
+  using Set = base::flat_set<MoveOnly>;
+
+  Set cont;
+  Set::iterator result = cont.insert(cont.cend(), MoveOnly(2));
+  EXPECT_EQ(cont.begin(), result);
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+  EXPECT_EQ(2, *result);
+
+  result = cont.insert(cont.cend(), MoveOnly(1));
+  EXPECT_EQ(cont.begin(), result);
+  EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+  EXPECT_EQ(1, *result);
+
+  result = cont.insert(cont.cend(), MoveOnly(3));
+  EXPECT_EQ(std::prev(cont.end()), result);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result);
+
+  result = cont.insert(cont.cend(), MoveOnly(3));
+  EXPECT_EQ(std::prev(cont.end()), result);
+  EXPECT_EQ(static_cast<Set::size_type>(3), cont.size());
+  EXPECT_EQ(3, *result);
+}
+
+// template <class InputIterator>
+//   void insert(InputIterator first, InputIterator last);
+
+TEST(FlatSet, InsertRange) {
+  using Set = base::flat_set<int>;
+
+  int input[] = {1, 1, 1, 2, 2, 2, 3, 3, 3};
+
+  Set cont;
+  cont.insert(MakeInputIterator(std::begin(input)),
+              MakeInputIterator(std::end(input)));
+  ExpectRange(cont, {1, 2, 3});
+}
+
+// void insert(initializer_list<value_type> il);
+
+TEST(FlatSet, InsertInitializerList) {
+  using Set = base::flat_set<int>;
+
+  Set cont = {10, 8};
+  cont.insert({1, 2, 3, 4, 5, 6});
+  ExpectRange(cont, {1, 2, 3, 4, 5, 6, 8, 10});
+}
+
+// template <class... Args>
+//   pair<iterator, bool> emplace(Args&&... args);
+
+TEST(FlatSet, Emplace) {
+  {
+    using Set = base::flat_set<Emplaceable>;
+
+    Set cont;
+    std::pair<Set::iterator, bool> result = cont.emplace();
+    EXPECT_TRUE(result.second);
+    EXPECT_EQ(cont.begin(), result.first);
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+    EXPECT_EQ(Emplaceable(), *cont.begin());
+
+    result = cont.emplace(2, 3.5);
+    EXPECT_TRUE(result.second);
+    EXPECT_EQ(std::next(cont.begin()), result.first);
+    EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+    EXPECT_EQ(Emplaceable(2, 3.5), *result.first);
+
+    result = cont.emplace(2, 3.5);
+    EXPECT_FALSE(result.second);
+    EXPECT_EQ(std::next(cont.begin()), result.first);
+    EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+    EXPECT_EQ(Emplaceable(2, 3.5), *result.first);
+  }
+  {
+    using Set = base::flat_set<int>;
+
+    Set cont;
+    std::pair<Set::iterator, bool> result = cont.emplace(2);
+    EXPECT_TRUE(result.second);
+    EXPECT_EQ(cont.begin(), result.first);
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+    EXPECT_EQ(2, *result.first);
+  }
+}
+
+// template <class... Args>
+//   iterator emplace_hint(const_iterator position, Args&&... args);
+
+TEST(FlatSet, EmplaceHint) {
+  {
+    using Set = base::flat_set<Emplaceable>;
+
+    Set cont;
+    Set::iterator result = cont.emplace_hint(cont.cend());
+    EXPECT_EQ(cont.begin(), result);
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+    EXPECT_EQ(Emplaceable(), *cont.begin());
+
+    result = cont.emplace_hint(cont.cend(), 2, 3.5);
+    EXPECT_EQ(std::next(cont.begin()), result);
+    EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+    EXPECT_EQ(Emplaceable(2, 3.5), *result);
+
+    result = cont.emplace_hint(cont.cbegin(), 2, 3.5);
+    EXPECT_EQ(std::next(cont.begin()), result);
+    EXPECT_EQ(static_cast<Set::size_type>(2), cont.size());
+    EXPECT_EQ(Emplaceable(2, 3.5), *result);
+  }
+  {
+    using Set = base::flat_set<int>;
+
+    Set cont;
+    Set::iterator result = cont.emplace_hint(cont.cend(), 2);
+    EXPECT_EQ(cont.begin(), result);
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.size());
+    EXPECT_EQ(2, *result);
+  }
+}
+
+// ----------------------------------------------------------------------------
+// Erase operations.
+
+// iterator erase(const_iterator position);
+
+TEST(FlatSet, EraseCIter) {
+  using Set = base::flat_set<int>;
+
+  Set cont{1, 2, 3, 4, 5, 6, 7, 8};
+
+  Set::iterator it = cont.erase(std::next(cont.cbegin(), 3));
+  EXPECT_EQ(std::next(cont.begin(), 3), it);
+  ExpectRange(cont, {1, 2, 3, 5, 6, 7, 8});
+
+  it = cont.erase(std::next(cont.cbegin(), 0));
+  EXPECT_EQ(cont.begin(), it);
+  ExpectRange(cont, {2, 3, 5, 6, 7, 8});
+
+  it = cont.erase(std::next(cont.cbegin(), 5));
+  EXPECT_EQ(cont.end(), it);
+  ExpectRange(cont, {2, 3, 5, 6, 7});
+
+  it = cont.erase(std::next(cont.cbegin(), 1));
+  EXPECT_EQ(std::next(cont.begin()), it);
+  ExpectRange(cont, {2, 5, 6, 7});
+
+  it = cont.erase(std::next(cont.cbegin(), 2));
+  EXPECT_EQ(std::next(cont.begin(), 2), it);
+  ExpectRange(cont, {2, 5, 7});
+
+  it = cont.erase(std::next(cont.cbegin(), 2));
+  EXPECT_EQ(std::next(cont.begin(), 2), it);
+  ExpectRange(cont, {2, 5});
+
+  it = cont.erase(std::next(cont.cbegin(), 0));
+  EXPECT_EQ(std::next(cont.begin(), 0), it);
+  ExpectRange(cont, {5});
+
+  it = cont.erase(cont.cbegin());
+  EXPECT_EQ(cont.begin(), it);
+  EXPECT_EQ(cont.end(), it);
+}
+
+// iterator erase(const_iterator first, const_iterator last);
+
+TEST(FlatSet, EraseCIterCIter) {
+  using Set = base::flat_set<int>;
+
+  Set cont{1, 2, 3, 4, 5, 6, 7, 8};
+
+  Set::iterator it =
+      cont.erase(std::next(cont.cbegin(), 5), std::next(cont.cbegin(), 5));
+  EXPECT_EQ(std::next(cont.begin(), 5), it);
+  ExpectRange(cont, {1, 2, 3, 4, 5, 6, 7, 8});
+
+  it = cont.erase(std::next(cont.cbegin(), 3), std::next(cont.cbegin(), 4));
+  EXPECT_EQ(std::next(cont.begin(), 3), it);
+  ExpectRange(cont, {1, 2, 3, 5, 6, 7, 8});
+
+  it = cont.erase(std::next(cont.cbegin(), 2), std::next(cont.cbegin(), 5));
+  EXPECT_EQ(std::next(cont.begin(), 2), it);
+  ExpectRange(cont, {1, 2, 7, 8});
+
+  it = cont.erase(std::next(cont.cbegin(), 0), std::next(cont.cbegin(), 2));
+  EXPECT_EQ(std::next(cont.begin(), 0), it);
+  ExpectRange(cont, {7, 8});
+
+  it = cont.erase(cont.cbegin(), cont.cend());
+  EXPECT_EQ(cont.begin(), it);
+  EXPECT_EQ(cont.end(), it);
+}
+
+// size_type erase(const key_type& k);
+
+TEST(FlatSet, EraseKey) {
+  using Set = base::flat_set<int>;
+
+  Set cont{1, 2, 3, 4, 5, 6, 7, 8};
+
+  EXPECT_EQ(static_cast<Set::size_type>(0), cont.erase(9));
+  ExpectRange(cont, {1, 2, 3, 4, 5, 6, 7, 8});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(4));
+  ExpectRange(cont, {1, 2, 3, 5, 6, 7, 8});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(1));
+  ExpectRange(cont, {2, 3, 5, 6, 7, 8});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(8));
+  ExpectRange(cont, {2, 3, 5, 6, 7});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(3));
+  ExpectRange(cont, {2, 5, 6, 7});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(6));
+  ExpectRange(cont, {2, 5, 7});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(7));
+  ExpectRange(cont, {2, 5});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(2));
+  ExpectRange(cont, {5});
+
+  EXPECT_EQ(static_cast<Set::size_type>(1), cont.erase(5));
+  ExpectRange(cont, {});
+}
+
+// ----------------------------------------------------------------------------
+// Comparators.
+
+// key_compare key_comp() const
+
+TEST(FlatSet, KeyComp) {
+  using Set = base::flat_set<int, std::greater<int>>;
+
+  Set cont{1, 2, 3, 4, 5};
+
+  EXPECT_TRUE(std::is_sorted(cont.begin(), cont.end(), cont.key_comp()));
+  cont.insert({6, 7, 8, 9, 10});
+  EXPECT_TRUE(std::is_sorted(cont.begin(), cont.end(), cont.key_comp()));
+}
+
+// value_compare value_comp() const
+
+TEST(FlatSet, ValueComp) {
+  using Set = base::flat_set<int, std::greater<int>>;
+
+  Set cont{1, 2, 3, 4, 5};
+
+  EXPECT_TRUE(std::is_sorted(cont.begin(), cont.end(), cont.value_comp()));
+  cont.insert({6, 7, 8, 9, 10});
+  EXPECT_TRUE(std::is_sorted(cont.begin(), cont.end(), cont.value_comp()));
+}
+
+// ----------------------------------------------------------------------------
+// Binary search operations.
+
+// size_type count(const key_type& k) const;
+
+TEST(FlatSet, Count) {
+  {
+    using Set = base::flat_set<int>;
+
+    const Set cont{5, 6, 7, 8, 9, 10, 11, 12};
+
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(5));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(6));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(7));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(8));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(9));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(10));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(11));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(12));
+    EXPECT_EQ(static_cast<Set::size_type>(0), cont.count(4));
+  }
+  {
+    using Set = base::flat_set<int, std::less<int>>;
+
+    const Set cont{5, 6, 7, 8, 9, 10, 11, 12};
+
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(5));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(6));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(7));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(8));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(9));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(10));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(11));
+    EXPECT_EQ(static_cast<Set::size_type>(1), cont.count(12));
+    EXPECT_EQ(static_cast<Set::size_type>(0), cont.count(4));
+  }
+}
+
+//       iterator find(const key_type& k);
+// const_iterator find(const key_type& k) const;
+
+TEST(FlatSet, Find) {
+  {
+    using Set = base::flat_set<int>;
+    {
+      Set cont{5, 6, 7, 8, 9, 10, 11, 12};
+
+      EXPECT_EQ(cont.begin(), cont.find(5));
+      EXPECT_EQ(std::next(cont.begin()), cont.find(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.find(7));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.find(8));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.find(9));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.find(10));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.find(11));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.find(12));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.find(4));
+    }
+    {
+      const Set cont{5, 6, 7, 8, 9, 10, 11, 12};
+
+      EXPECT_EQ(cont.begin(), cont.find(5));
+      EXPECT_EQ(std::next(cont.begin()), cont.find(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.find(7));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.find(8));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.find(9));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.find(10));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.find(11));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.find(12));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.find(4));
+    }
+  }
+  {
+    using Set = base::flat_set<int, std::less<int>>;
+
+    Set cont{5, 6, 7, 8, 9, 10, 11, 12};
+
+    EXPECT_EQ(cont.begin(), cont.find(5));
+    EXPECT_EQ(std::next(cont.begin()), cont.find(6));
+    EXPECT_EQ(std::next(cont.begin(), 2), cont.find(7));
+    EXPECT_EQ(std::next(cont.begin(), 3), cont.find(8));
+    EXPECT_EQ(std::next(cont.begin(), 4), cont.find(9));
+    EXPECT_EQ(std::next(cont.begin(), 5), cont.find(10));
+    EXPECT_EQ(std::next(cont.begin(), 6), cont.find(11));
+    EXPECT_EQ(std::next(cont.begin(), 7), cont.find(12));
+    EXPECT_EQ(std::next(cont.begin(), 8), cont.find(4));
+  }
+}
+
+// pair<iterator,iterator>             equal_range(const key_type& k);
+// pair<const_iterator,const_iterator> equal_range(const key_type& k) const;
+
+TEST(FlatSet, EqualRange) {
+  {
+    using Set = base::flat_set<int>;
+    {
+      Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      std::pair<Set::iterator, Set::iterator> result = cont.equal_range(5);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+      result = cont.equal_range(7);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+      result = cont.equal_range(9);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+      result = cont.equal_range(11);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+      result = cont.equal_range(13);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+      result = cont.equal_range(15);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+      result = cont.equal_range(17);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+      result = cont.equal_range(19);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+      result = cont.equal_range(4);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.second);
+      result = cont.equal_range(6);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+      result = cont.equal_range(8);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+      result = cont.equal_range(10);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+      result = cont.equal_range(12);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+      result = cont.equal_range(14);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+      result = cont.equal_range(16);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+      result = cont.equal_range(18);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+      result = cont.equal_range(20);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+    }
+    {
+      const Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      std::pair<Set::const_iterator, Set::const_iterator> result =
+          cont.equal_range(5);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+      result = cont.equal_range(7);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+      result = cont.equal_range(9);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+      result = cont.equal_range(11);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+      result = cont.equal_range(13);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+      result = cont.equal_range(15);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+      result = cont.equal_range(17);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+      result = cont.equal_range(19);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+      result = cont.equal_range(4);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 0), result.second);
+      result = cont.equal_range(6);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+      result = cont.equal_range(8);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+      result = cont.equal_range(10);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+      result = cont.equal_range(12);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+      result = cont.equal_range(14);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+      result = cont.equal_range(16);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+      result = cont.equal_range(18);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+      result = cont.equal_range(20);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.first);
+      EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+    }
+  }
+
+  {
+    using Set = base::flat_set<int, std::less<int>>;
+
+    Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+    std::pair<Set::iterator, Set::iterator> result = cont.equal_range(5);
+    EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+    result = cont.equal_range(7);
+    EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+    result = cont.equal_range(9);
+    EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+    result = cont.equal_range(11);
+    EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+    result = cont.equal_range(13);
+    EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+    result = cont.equal_range(15);
+    EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+    result = cont.equal_range(17);
+    EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+    result = cont.equal_range(19);
+    EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+    result = cont.equal_range(4);
+    EXPECT_EQ(std::next(cont.begin(), 0), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 0), result.second);
+    result = cont.equal_range(6);
+    EXPECT_EQ(std::next(cont.begin(), 1), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 1), result.second);
+    result = cont.equal_range(8);
+    EXPECT_EQ(std::next(cont.begin(), 2), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 2), result.second);
+    result = cont.equal_range(10);
+    EXPECT_EQ(std::next(cont.begin(), 3), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 3), result.second);
+    result = cont.equal_range(12);
+    EXPECT_EQ(std::next(cont.begin(), 4), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 4), result.second);
+    result = cont.equal_range(14);
+    EXPECT_EQ(std::next(cont.begin(), 5), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 5), result.second);
+    result = cont.equal_range(16);
+    EXPECT_EQ(std::next(cont.begin(), 6), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 6), result.second);
+    result = cont.equal_range(18);
+    EXPECT_EQ(std::next(cont.begin(), 7), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 7), result.second);
+    result = cont.equal_range(20);
+    EXPECT_EQ(std::next(cont.begin(), 8), result.first);
+    EXPECT_EQ(std::next(cont.begin(), 8), result.second);
+  }
+}
+
+//       iterator lower_bound(const key_type& k);
+// const_iterator lower_bound(const key_type& k) const;
+
+TEST(FlatSet, LowerBound) {
+  {
+    using Set = base::flat_set<int>;
+    {
+      Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      EXPECT_EQ(cont.begin(), cont.lower_bound(5));
+      EXPECT_EQ(std::next(cont.begin()), cont.lower_bound(7));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(9));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(11));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(13));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(15));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(17));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(19));
+      EXPECT_EQ(std::next(cont.begin(), 0), cont.lower_bound(4));
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.lower_bound(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(8));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(10));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(12));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(14));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(16));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(18));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.lower_bound(20));
+    }
+    {
+      const Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      EXPECT_EQ(cont.begin(), cont.lower_bound(5));
+      EXPECT_EQ(std::next(cont.begin()), cont.lower_bound(7));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(9));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(11));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(13));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(15));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(17));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(19));
+      EXPECT_EQ(std::next(cont.begin(), 0), cont.lower_bound(4));
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.lower_bound(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(8));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(10));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(12));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(14));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(16));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(18));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.lower_bound(20));
+    }
+  }
+  {
+    using Set = base::flat_set<int, std::less<int>>;
+
+    Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+    EXPECT_EQ(cont.begin(), cont.lower_bound(5));
+    EXPECT_EQ(std::next(cont.begin()), cont.lower_bound(7));
+    EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(9));
+    EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(11));
+    EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(13));
+    EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(15));
+    EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(17));
+    EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(19));
+    EXPECT_EQ(std::next(cont.begin(), 0), cont.lower_bound(4));
+    EXPECT_EQ(std::next(cont.begin(), 1), cont.lower_bound(6));
+    EXPECT_EQ(std::next(cont.begin(), 2), cont.lower_bound(8));
+    EXPECT_EQ(std::next(cont.begin(), 3), cont.lower_bound(10));
+    EXPECT_EQ(std::next(cont.begin(), 4), cont.lower_bound(12));
+    EXPECT_EQ(std::next(cont.begin(), 5), cont.lower_bound(14));
+    EXPECT_EQ(std::next(cont.begin(), 6), cont.lower_bound(16));
+    EXPECT_EQ(std::next(cont.begin(), 7), cont.lower_bound(18));
+    EXPECT_EQ(std::next(cont.begin(), 8), cont.lower_bound(20));
+  }
+}
+
+//       iterator upper_bound(const key_type& k);
+// const_iterator upper_bound(const key_type& k) const;
+
+TEST(FlatSet, UpperBound) {
+  {
+    using Set = base::flat_set<int>;
+    {
+      Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(5));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(7));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(9));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(11));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(13));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(15));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(17));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(19));
+      EXPECT_EQ(std::next(cont.begin(), 0), cont.upper_bound(4));
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(8));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(10));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(12));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(14));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(16));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(18));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(20));
+    }
+    {
+      const Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(5));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(7));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(9));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(11));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(13));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(15));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(17));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(19));
+      EXPECT_EQ(std::next(cont.begin(), 0), cont.upper_bound(4));
+      EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(6));
+      EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(8));
+      EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(10));
+      EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(12));
+      EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(14));
+      EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(16));
+      EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(18));
+      EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(20));
+    }
+  }
+  {
+    using Set = base::flat_set<int, std::less<int>>;
+
+    Set cont{5, 7, 9, 11, 13, 15, 17, 19};
+
+    EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(5));
+    EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(7));
+    EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(9));
+    EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(11));
+    EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(13));
+    EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(15));
+    EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(17));
+    EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(19));
+    EXPECT_EQ(std::next(cont.begin(), 0), cont.upper_bound(4));
+    EXPECT_EQ(std::next(cont.begin(), 1), cont.upper_bound(6));
+    EXPECT_EQ(std::next(cont.begin(), 2), cont.upper_bound(8));
+    EXPECT_EQ(std::next(cont.begin(), 3), cont.upper_bound(10));
+    EXPECT_EQ(std::next(cont.begin(), 4), cont.upper_bound(12));
+    EXPECT_EQ(std::next(cont.begin(), 5), cont.upper_bound(14));
+    EXPECT_EQ(std::next(cont.begin(), 6), cont.upper_bound(16));
+    EXPECT_EQ(std::next(cont.begin(), 7), cont.upper_bound(18));
+    EXPECT_EQ(std::next(cont.begin(), 8), cont.upper_bound(20));
+  }
+}
+
+// ----------------------------------------------------------------------------
+// General operations.
+
+// void swap(flat_set& x)
+// void swap(flat_set& x, flat_set& y)
+
+TEST(FlatSetOurs, Swap) {
+  using Set = base::flat_set<int>;
+  Set x{1, 2, 3};
+  Set y{4};
+  swap(x, y);
+  ExpectRange(x, {4});
+  ExpectRange(y, {1, 2, 3});
+
+  y.swap(x);
+  ExpectRange(x, {1, 2, 3});
+  ExpectRange(y, {4});
+}
+
+// bool operator==(const flat_set& x, const flat_set& y)
+// bool operator!=(const flat_set& x, const flat_set& y)
+// bool operator<(const flat_set& x, const flat_set& y)
+// bool operator>(const flat_set& x, const flat_set& y)
+// bool operator<=(const flat_set& x, const flat_set& y)
+// bool operator>=(const flat_set& x, const flat_set& y)
+
+TEST(FlatSet, Comparison) {
+  // Provided comparator does not participate in comparison.
+  using Cmp = std::greater<int>;
+  using Set = base::flat_set<int, Cmp>;
+
+  Set biggest{3};
+  Set smallest{1};
+  Set middle{1, 2};
+
+  EXPECT_EQ(biggest, biggest);
+  EXPECT_NE(biggest, smallest);
+  EXPECT_LT(smallest, middle);
+  EXPECT_LE(smallest, middle);
+  EXPECT_LE(middle, middle);
+  EXPECT_GT(biggest, middle);
+  EXPECT_GE(biggest, middle);
+  EXPECT_GE(biggest, biggest);
+}