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Enable inheriting from formatter<std::string_view> #4055

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merged 1 commit into from
Jul 14, 2024
Merged

Enable inheriting from formatter<std::string_view> #4055

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12 changes: 9 additions & 3 deletions include/fmt/format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3978,9 +3978,15 @@ struct formatter<T, Char, enable_if_t<detail::has_format_as<T>::value>>
}
};

#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> {}
#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> { \
template <typename FormatContext> \
auto format(Type value, FormatContext& ctx) const -> decltype(ctx.out()) { \
using base = formatter<Base, Char>; \
return base::format(value, ctx); \
} \
}

FMT_FORMAT_AS(signed char, int);
FMT_FORMAT_AS(unsigned char, unsigned);
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14 changes: 14 additions & 0 deletions test/format-test.cc
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Expand Up @@ -1650,6 +1650,20 @@ TEST(format_test, format_explicitly_convertible_to_std_string_view) {
EXPECT_EQ("'foo'",
fmt::format("{}", explicitly_convertible_to_std_string_view()));
}

struct convertible_to_std_string_view {
operator std::string_view() const noexcept { return "Hi there"; }
};
FMT_BEGIN_NAMESPACE
template <>
class formatter<convertible_to_std_string_view>
: public formatter<std::string_view> {};
FMT_END_NAMESPACE

TEST(format_test, format_implicitly_convertible_and_inherits_string_view) {
static_assert(fmt::is_formattable<convertible_to_std_string_view>{}, "");
EXPECT_EQ("Hi there", fmt::format("{}", convertible_to_std_string_view{}));
}
#endif

class Answer {};
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