2 files changed, 31 insertions, 28 deletions

diff --git a/absl/strings/internal/resize_uninitialized.h b/absl/strings/internal/resize_uninitialized.h
index a94e0547..c2da0da9 100644
--- a/absl/strings/internal/resize_uninitialized.h
+++ b/absl/strings/internal/resize_uninitialized.h
@@ -18,6 +18,7 @@
 #define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
 
 #include <string>
+#include <type_traits>
 #include <utility>
 
 #include "absl/base/port.h"
@@ -27,22 +28,24 @@ namespace absl {
 namespace strings_internal {
 
 // Is a subclass of true_type or false_type, depending on whether or not
-// T has a resize_uninitialized member.
-template <typename T, typename = void>
-struct HasResizeUninitialized : std::false_type {};
-template <typename T>
-struct HasResizeUninitialized<
-    T, absl::void_t<decltype(std::declval<T>().resize_uninitialized(237))>>
-    : std::true_type {};
+// T has a __resize_default_init member.
+template <typename string_type, typename = void>
+struct ResizeUninitializedTraits {
+  using HasMember = std::false_type;
+  static void Resize(string_type* s, size_t new_size) { s->resize(new_size); }
+};
 
+// __resize_default_init is provided by libc++ >= 8.0 and by Google's internal
+// ::string implementation.
 template <typename string_type>
-void ResizeUninit(string_type* s, size_t new_size, std::true_type) {
-  s->resize_uninitialized(new_size);
-}
-template <typename string_type>
-void ResizeUninit(string_type* s, size_t new_size, std::false_type) {
-  s->resize(new_size);
-}
+struct ResizeUninitializedTraits<
+    string_type, absl::void_t<decltype(std::declval<string_type&>()
+                                           .__resize_default_init(237))> > {
+  using HasMember = std::true_type;
+  static void Resize(string_type* s, size_t new_size) {
+    s->__resize_default_init(new_size);
+  }
+};
 
 // Returns true if the string implementation supports a resize where
 // the new characters added to the string are left untouched.
@@ -51,7 +54,7 @@ void ResizeUninit(string_type* s, size_t new_size, std::false_type) {
 // the previous function.)
 template <typename string_type>
 inline constexpr bool STLStringSupportsNontrashingResize(string_type*) {
-  return HasResizeUninitialized<string_type>();
+  return ResizeUninitializedTraits<string_type>::HasMember::value;
 }
 
 // Like str->resize(new_size), except any new characters added to "*str" as a
@@ -60,7 +63,7 @@ inline constexpr bool STLStringSupportsNontrashingResize(string_type*) {
 // store of the string with known data. Uses a Google extension to ::string.
 template <typename string_type, typename = void>
 inline void STLStringResizeUninitialized(string_type* s, size_t new_size) {
-  ResizeUninit(s, new_size, HasResizeUninitialized<string_type>());
+  ResizeUninitializedTraits<string_type>::Resize(s, new_size);
 }
 
 }  // namespace strings_internal
diff --git a/absl/strings/internal/resize_uninitialized_test.cc b/absl/strings/internal/resize_uninitialized_test.cc
index ad282efc..43aece8d 100644
--- a/absl/strings/internal/resize_uninitialized_test.cc
+++ b/absl/strings/internal/resize_uninitialized_test.cc
@@ -24,44 +24,44 @@ struct resizable_string {
   void resize(size_t) { resize_call_count += 1; }
 };
 
-int resize_uninitialized_call_count = 0;
+int resize_default_init_call_count = 0;
 
-struct resize_uninitializable_string {
+struct resize_default_init_string {
   void resize(size_t) { resize_call_count += 1; }
-  void resize_uninitialized(size_t) { resize_uninitialized_call_count += 1; }
+  void __resize_default_init(size_t) { resize_default_init_call_count += 1; }
 };
 
 TEST(ResizeUninit, WithAndWithout) {
   resize_call_count = 0;
-  resize_uninitialized_call_count = 0;
+  resize_default_init_call_count = 0;
   {
     resizable_string rs;
 
     EXPECT_EQ(resize_call_count, 0);
-    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
     EXPECT_FALSE(
         absl::strings_internal::STLStringSupportsNontrashingResize(&rs));
     EXPECT_EQ(resize_call_count, 0);
-    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
     absl::strings_internal::STLStringResizeUninitialized(&rs, 237);
     EXPECT_EQ(resize_call_count, 1);
-    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
   }
 
   resize_call_count = 0;
-  resize_uninitialized_call_count = 0;
+  resize_default_init_call_count = 0;
   {
-    resize_uninitializable_string rus;
+    resize_default_init_string rus;
 
     EXPECT_EQ(resize_call_count, 0);
-    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
     EXPECT_TRUE(
         absl::strings_internal::STLStringSupportsNontrashingResize(&rus));
     EXPECT_EQ(resize_call_count, 0);
-    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
     absl::strings_internal::STLStringResizeUninitialized(&rus, 237);
     EXPECT_EQ(resize_call_count, 0);
-    EXPECT_EQ(resize_uninitialized_call_count, 1);
+    EXPECT_EQ(resize_default_init_call_count, 1);
   }
 }