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added formatter for std::expected
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dominicpoeschko committed Jan 31, 2024
1 parent 71a4a8d commit cfe55c1
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49 changes: 49 additions & 0 deletions include/fmt/std.h
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,9 @@
# if FMT_HAS_INCLUDE(<optional>)
# include <optional>
# endif
# if FMT_HAS_INCLUDE(<expected>)
# include <expected>
# endif
#endif

#if FMT_CPLUSPLUS > 201703L && FMT_HAS_INCLUDE(<source_location>)
Expand Down Expand Up @@ -242,6 +245,52 @@ struct formatter<std::optional<T>, Char,
FMT_END_NAMESPACE
#endif // __cpp_lib_optional

#ifdef __cpp_lib_expected
FMT_BEGIN_NAMESPACE
namespace detail {

template <typename Char, typename OutputIt, typename T>
auto write_expected_alternative(OutputIt out, const T& v) -> OutputIt {
if constexpr (has_to_string_view<T>::value)
return write_escaped_string<Char>(out, detail::to_string_view(v));
else if constexpr (std::is_same_v<T, Char>)
return write_escaped_char(out, v);
else
return write<Char>(out, v);
}

} // namespace detail

FMT_EXPORT
template <typename T, typename E, typename Char>
struct formatter<
std::expected<T, E>, Char,
std::enable_if_t<std::conjunction_v<
is_formattable<T, Char>, is_formattable<E, Char>>>> {
template <typename ParseContext>
FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
return ctx.begin();
}

template <typename FormatContext>
auto format(const std::expected<T, E>& value, FormatContext& ctx) const
-> decltype(ctx.out()) {
auto out = ctx.out();

if(value.has_value()) {
out = detail::write<Char>(out, "expected(");
out = detail::write_expected_alternative<Char>(out, value.value());
} else {
out = detail::write<Char>(out, "unexpected(");
out = detail::write_expected_alternative<Char>(out, value.error());
}
*out++ = ')';
return out;
}
};
FMT_END_NAMESPACE
#endif // __cpp_lib_expected

#ifdef __cpp_lib_source_location
FMT_BEGIN_NAMESPACE
FMT_EXPORT
Expand Down
20 changes: 20 additions & 0 deletions test/std-test.cc
Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,26 @@ TEST(std_test, optional) {
#endif
}

TEST(std_test, expected) {
#ifdef __cpp_lib_expected
EXPECT_EQ(fmt::format("{}", std::expected<int, int>{1}), "expected(1)");
EXPECT_EQ(fmt::format("{}", std::expected<int, int>{std::unexpected(1)}), "unexpected(1)");
EXPECT_EQ(fmt::format("{}", std::expected<std::string, int>{"test"}), "expected(\"test\")");
EXPECT_EQ(fmt::format("{}", std::expected<int, std::string>{std::unexpected("test")}), "unexpected(\"test\")");
EXPECT_EQ(fmt::format("{}", std::expected<char, int>{'a'}), "expected('a')");
EXPECT_EQ(fmt::format("{}", std::expected<int, char>{std::unexpected('a')}), "unexpected('a')");

struct unformattable1 {};
struct unformattable2 {};
EXPECT_FALSE((fmt::is_formattable<unformattable1>::value));
EXPECT_FALSE((fmt::is_formattable<unformattable2>::value));
EXPECT_FALSE((fmt::is_formattable<std::expected<unformattable1, unformattable2>>::value));
EXPECT_FALSE((fmt::is_formattable<std::expected<unformattable1, int>>::value));
EXPECT_FALSE((fmt::is_formattable<std::expected<int, unformattable2>>::value));
EXPECT_TRUE((fmt::is_formattable<std::expected<int, int>>::value));
#endif
}

namespace my_nso {
enum class my_number {
one,
Expand Down

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