Add std::complex formatter

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

include/fmt/std.h

@@ -10,6 +10,7 @@
 
 #include <atomic>
 #include <bitset>
+#include <complex>
 #include <cstdlib>
 #include <exception>
 #include <memory>
@@ -585,5 +586,31 @@ struct formatter<std::atomic_flag, Char> : formatter<bool, Char> {
 };
 #endif  // __cpp_lib_atomic_flag_test
 
+FMT_EXPORT
+template <typename F, typename Char>
+struct formatter<std::complex<F>, Char> : nested_formatter<F, Char> {
+ private:
+  // Functor because C++11 doesn't support generic lambdas.
+  struct writer {
+    const formatter<std::complex<F>, Char>* f;
+    const std::complex<F>& c;
+
+    template <typename OutputIt>
+    FMT_CONSTEXPR auto operator()(OutputIt out) -> OutputIt {
+      auto format =
+          detail::string_literal<Char, '(', '{', '}', ',', '{', '}', ')'>{};
+      return fmt::format_to(out, basic_string_view<Char>(format),
+                            f->nested(c.real()), f->nested(c.imag()));
+    }
+  };
+
+ public:
+  template <typename FormatContext>
+  auto format(const std::complex<F>& c, FormatContext& ctx) const
+      -> decltype(ctx.out()) {
+    return this->write_padded(ctx, writer{this, c});
+  }
+};
+
 FMT_END_NAMESPACE
 #endif  // FMT_STD_H_

test/std-test.cc

@@ -65,6 +65,12 @@ TEST(std_test, thread_id) {
   EXPECT_FALSE(fmt::format("{}", std::this_thread::get_id()).empty());
 }
 
+TEST(std_test, complex) {
+  EXPECT_EQ(fmt::format("{}", std::complex<double>(1, 2.2)), "(1,2.2)");
+  EXPECT_EQ(fmt::format("{:>20.2f}", std::complex<double>(1, 2.2)),
+            "         (1.00,2.20)");
+}
+
 #ifdef __cpp_lib_source_location
 TEST(std_test, source_location) {
   std::source_location loc = std::source_location::current();

test/xchar-test.cc

@@ -562,49 +562,6 @@ TEST(locale_test, int_formatter) {
   EXPECT_EQ(fmt::to_string(buf), "12,345");
 }
 
-FMT_BEGIN_NAMESPACE
-template <class charT> struct formatter<std::complex<double>, charT> {
- private:
-  detail::dynamic_format_specs<char> specs_;
-
- public:
-  FMT_CONSTEXPR typename basic_format_parse_context<charT>::iterator parse(
-      basic_format_parse_context<charT>& ctx) {
-    auto end = parse_format_specs(ctx.begin(), ctx.end(), specs_, ctx,
-                                  detail::type::float_type);
-    detail::parse_float_type_spec(specs_);
-    return end;
-  }
-
-  template <class FormatContext>
-  typename FormatContext::iterator format(const std::complex<double>& c,
-                                          FormatContext& ctx) const {
-    auto specs = specs_;
-    detail::handle_dynamic_spec<detail::precision_checker>(
-        specs.precision, specs.precision_ref, ctx);
-    auto fspecs = std::string();
-    if (specs.precision > 0) fspecs = fmt::format(".{}", specs.precision);
-    if (specs.type == presentation_type::fixed) fspecs += 'f';
-    auto real = fmt::format(ctx.locale().template get<std::locale>(),
-                            fmt::runtime("{:" + fspecs + "}"), c.real());
-    auto imag = fmt::format(ctx.locale().template get<std::locale>(),
-                            fmt::runtime("{:" + fspecs + "}"), c.imag());
-    auto fill_align_width = std::string();
-    if (specs.width > 0) fill_align_width = fmt::format(">{}", specs.width);
-    return fmt::format_to(ctx.out(), runtime("{:" + fill_align_width + "}"),
-                          c.real() != 0 ? fmt::format("({}+{}i)", real, imag)
-                                        : fmt::format("{}i", imag));
-  }
-};
-FMT_END_NAMESPACE
-
-TEST(locale_test, complex) {
-  std::string s = fmt::format("{}", std::complex<double>(1, 2));
-  EXPECT_EQ(s, "(1+2i)");
-  EXPECT_EQ(fmt::format("{:.2f}", std::complex<double>(1, 2)), "(1.00+2.00i)");
-  EXPECT_EQ(fmt::format("{:8}", std::complex<double>(1, 2)), "  (1+2i)");
-}
-
 TEST(locale_test, chrono_weekday) {
   auto loc = get_locale("es_ES.UTF-8", "Spanish_Spain.1252");
   auto loc_old = std::locale::global(loc);
@@ -625,6 +582,13 @@ TEST(locale_test, sign) {
   EXPECT_EQ(fmt::format(std::locale(), L"{:L}", -50), L"-50");
 }
 
+TEST(std_test_xchar, complex) {
+  auto s = fmt::format(L"{}", std::complex<double>(1, 2));
+  EXPECT_EQ(s, L"(1,2)");
+  EXPECT_EQ(fmt::format(L"{:.2f}", std::complex<double>(1, 2)), L"(1.00,2.00)");
+  EXPECT_EQ(fmt::format(L"{:8}", std::complex<double>(1, 2)), L"(1,2)   ");
+}
+
 TEST(std_test_xchar, optional) {
 #  ifdef __cpp_lib_optional
   EXPECT_EQ(fmt::format(L"{}", std::optional{L'C'}), L"optional(\'C\')");