Improving flat containers interface.

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
index dc024fcf0a9729a15d4987e3980da46306a6b143..af133638bee0b7421fd987bb8591de9d8e4c718c 100644
--- a/base/containers/flat_set_unittest.cc
+++ b/base/containers/flat_set_unittest.cc
@@ -7,8 +7,9 @@
 #include <string>
 #include <vector>
 
-#include "base/containers/container_test_utils.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/test/move_only_int.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -20,6 +21,35 @@ using ::testing::ElementsAre;
 
 namespace base {
 
+namespace {
+
+struct UniquePtrComparator {
+  // Mark your comparison as transparent.
+  using is_transparent = int;
+
+  template <typename T>
+  bool operator()(const std::unique_ptr<T>& lhs,
+                  const std::unique_ptr<T>& rhs) const {
+    return lhs < rhs;
+  }
+
+  template <typename T>
+  bool operator()(const T* lhs, const std::unique_ptr<T>& rhs) const {
+    return lhs < rhs.get();
+  }
+
+  template <typename T>
+  bool operator()(const std::unique_ptr<T>& lhs, const T* rhs) const {
+    return lhs.get() < rhs;
+  }
+};
+
+// Declare a typedef.
+template <typename T>
+using UniquePtrSet = base::flat_set<std::unique_ptr<T>, UniquePtrComparator>;
+
+}  // namespace
+
 TEST(FlatSet, IncompleteType) {
   struct A {
     using Set = flat_set<A>;
@@ -90,4 +120,46 @@ TEST(FlatSet, CopySwap) {
   EXPECT_THAT(copy, ElementsAre(1, 2));
 }
 
+TEST(FlatSet, UsingTransparentCompare) {
+  using ExplicitInt = base::MoveOnlyInt;
+  base::flat_set<ExplicitInt> s;
+  const auto& s1 = s;
+  int x = 0;
+
+  // Check if we can use lookup functions without converting to key_type.
+  // Correctness is checked in flat_tree tests.
+  s.count(x);
+  s1.count(x);
+  s.find(x);
+  s1.find(x);
+  s.equal_range(x);
+  s1.equal_range(x);
+  s.lower_bound(x);
+  s1.lower_bound(x);
+  s.upper_bound(x);
+  s1.upper_bound(x);
+  s.erase(x);
+
+  // Check if we broke overload resolution.
+  s.emplace(0);
+  s.emplace(1);
+  s.erase(s.begin());
+  s.erase(s.cbegin());
+}
+
+TEST(FlatSet, Examples) {
+  // Collect data.
+  std::vector<std::unique_ptr<int>> ptr_vec;
+  ptr_vec.reserve(5);
+  std::generate_n(std::back_inserter(ptr_vec), 5,
+                  [] { return base::MakeUnique<int>(0); });
+
+  // Construct set.
+  UniquePtrSet<int> ptr_set(std::move(ptr_vec), base::KEEP_FIRST_OF_DUPES);
+
+  // Use it with plain pointers.
+  int* ptr = ptr_set.begin()->get();
+  EXPECT_TRUE(ptr_set.find(ptr) == ptr_set.begin());
+}
+
 }  // namespace base