Make buffer_appender default-constructible when back_insert_iterator is

fmtlib · Apr 1, 2021 · c62e4c3 · c62e4c3
1 parent 0d6b70d
commit c62e4c3
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Showing 2 changed files with 18 additions and 1 deletion.
diff --git a/include/fmt/core.h b/include/fmt/core.h
@@ -877,7 +877,7 @@ class buffer_appender : public std::back_insert_iterator<buffer<T>> {
   using base = std::back_insert_iterator<buffer<T>>;
 
  public:
-  explicit buffer_appender(buffer<T>& buf) : base(buf) {}
+  using std::back_insert_iterator<buffer<T>>::back_insert_iterator;
   buffer_appender(base it) : base(it) {}
 
   buffer_appender& operator++() {

diff --git a/test/format-test.cc b/test/format-test.cc
@@ -217,6 +217,23 @@ static void check_move_buffer(
   EXPECT_EQ(alloc, buffer2.get_allocator().get());
 }
 
+TEST(BufferAppenderTest, BufferAppenderDefaultConstruct) {
+  // back_insert_iterator is not default-constructible before C++20, so
+  // buffer_appender can only be default-constructible when back_insert_iterator
+  // is.
+  static_assert(
+      std::is_default_constructible<
+          std::back_insert_iterator<fmt::detail::buffer<char>>>::value ==
+      std::is_default_constructible<fmt::detail::buffer_appender<char>>::value,
+      "");
+}
+
+#ifdef __cpp_lib_ranges
+TEST(BufferAppenderTest, BufferAppenderOutputIterator) {
+  static_assert(std::output_iterator<fmt::detail::buffer_appender<char>, char>);
+}
+#endif
+
 TEST(MemoryBufferTest, MoveCtorInlineBuffer) {
   std::allocator<char> alloc;
   basic_memory_buffer<char, 5, std_allocator> buffer((std_allocator(&alloc)));