Add std::optional

fmtlib · Feb 12, 2023 · fc57abb · fc57abb
1 parent 655046d
commit fc57abb
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Showing 2 changed files with 73 additions and 0 deletions.
diff --git a/include/fmt/std.h b/include/fmt/std.h
@@ -29,6 +29,9 @@
 #  if FMT_HAS_INCLUDE(<variant>)
 #    include <variant>
 #  endif
+#  if FMT_HAS_INCLUDE(<optional>)
+#    include <optional>
+#  endif
 #endif
 
 // GCC 4 does not support FMT_HAS_INCLUDE.
@@ -91,6 +94,41 @@ template <typename Char>
 struct formatter<std::thread::id, Char> : basic_ostream_formatter<Char> {};
 FMT_END_NAMESPACE
 
+#ifdef __cpp_lib_optional
+FMT_BEGIN_NAMESPACE
+template <class T, typename Char>
+struct formatter<std::optional<T>, Char,
+    std::enable_if_t<is_formattable<T>::value>> {
+  formatter<T, Char> underlying_;
+  static constexpr basic_string_view<Char> OPTION = detail::string_literal<Char, 'O','p','t','i','o','n','('>{};
+  static constexpr basic_string_view<Char> EMPTY = detail::string_literal<Char, 'E','m','p','t','y'>{};
+
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext& ctx) {
+    return underlying_.parse(ctx);
+  }
+  template <typename FormatContext>
+  auto format(std::optional<T> const& opt, FormatContext& ctx) const
+  -> decltype(ctx.out()) {
+    if (opt) {
+      auto out = ctx.out();
+      out = detail::write<Char>(out, OPTION);
+      if constexpr (detail::is_string<T>::value)
+        out = detail::write_escaped_string<Char>(out, detail::to_string_view(*opt));
+      else if constexpr (std::is_same_v<T, char>)
+        out = detail::write_escaped_char<Char>(out, *opt);
+      else {
+        ctx.advance_to(out);
+        out = underlying_.format(*opt, ctx);
+      }
+      return detail::write(out, ')');
+    }
+    return detail::write<Char>(ctx.out(), EMPTY);
+  }
+};
+FMT_END_NAMESPACE
+#endif // __cpp_lib_optional
+
 #ifdef __cpp_lib_variant
 FMT_BEGIN_NAMESPACE
 template <typename Char> struct formatter<std::monostate, Char> {

diff --git a/test/std-test.cc b/test/std-test.cc
@@ -6,6 +6,7 @@
 // For the license information refer to format.h.
 
 #include "fmt/std.h"
+#include "fmt/xchar.h"
 
 #include <string>
 #include <vector>
@@ -50,6 +51,40 @@ TEST(std_test, thread_id) {
   EXPECT_FALSE(fmt::format("{}", std::this_thread::get_id()).empty());
 }
 
+TEST(std_test, optional) {
+#ifdef __cpp_lib_optional
+  EXPECT_EQ(fmt::format(
+    L"{}", std::optional<int>{}),
+    L"Empty");
+  EXPECT_EQ(fmt::format(
+    "{}", std::vector{std::optional{1}, std::optional{2}, std::optional{3}}),
+    "[Option(1), Option(2), Option(3)]");
+  EXPECT_EQ(fmt::format(
+    "{:#x}", std::optional<std::optional<int>>{std::optional{1}}),
+    "Option(Option(0x1))");
+  EXPECT_EQ(fmt::format(
+    "{::d}", std::vector{'h', 'e', 'l', 'l', 'o'}),
+    "[104, 101, 108, 108, 111]");
+  EXPECT_EQ(fmt::format(
+    "{}", std::optional{std::string{"string"}}),
+    "Option(\"string\")");
+  EXPECT_EQ(fmt::format(
+    "{0:>{1}}", std::optional{'C'}),
+    "Option(\'C\')");
+  EXPECT_EQ(fmt::format(
+    "{:.{}f}", std::optional{3.14}, 1),
+    "Option(3.1)");
+  EXPECT_EQ(fmt::format(
+    "int: {0:d};  hex: {0:x};  oct: {0:o}; bin: {0:b}", std::optional{42}),
+    "int: Option(42);  hex: Option(2a);  oct: Option(52); bin: Option(101010)");
+
+  struct unformattable {};
+  EXPECT_FALSE((fmt::is_formattable<unformattable>::value));
+  EXPECT_FALSE((fmt::is_formattable<std::optional<unformattable>>::value));
+  EXPECT_TRUE((fmt::is_formattable<std::optional<int>>::value));
+  #endif
+}
+
 TEST(std_test, variant) {
 #ifdef __cpp_lib_variant
   EXPECT_EQ(fmt::format("{}", std::monostate{}), "monostate");