rok commented on code in PR #51216:
URL: https://github.com/apache/arrow/pull/51216#discussion_r4040097611
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cpp/src/arrow/util/chrono_internal.h:
##########
@@ -151,22 +127,172 @@ inline const time_zone* locate_zone(std::string_view
tz_name) {
inline const time_zone* current_zone() { return std::chrono::current_zone(); }
-// Formatting support - streams directly using C++20 std::vformat_to
-// Provides: direct streaming, stream state preservation, chaining, rich
format specifiers
+namespace detail {
+
+// Argument positions passed to std::vformat by to_stream below.
+enum class FormatArgument : char {
+ ZonedTime = '0',
+ TimeOfDay = '1',
+ TimeOfDayCount = '2',
+};
+
+template <typename CharT>
+void AppendEscapedLiteral(std::basic_string<CharT>* out, CharT value) {
+ out->push_back(value);
+ if (value == CharT{'{'} || value == CharT{'}'}) {
+ out->push_back(value);
+ }
+}
+
+// These are the directives accepted by Arrow's existing strftime syntax. Treat
+// all others as literals to preserve compatibility.
+template <typename CharT>
+bool IsSupportedStrftimeSpecifier(CharT modifier, CharT specifier) {
+ const auto contains = [specifier](const char* candidates) {
+ for (; *candidates != '\0'; ++candidates) {
+ if (specifier == static_cast<CharT>(*candidates)) return true;
+ }
+ return false;
+ };
+ if (modifier == CharT{}) {
+ return contains("aAbBhcCxdeDFgGHIjmMprRSTuUVWwXyYzZ");
+ }
+ if (modifier == CharT{'E'}) {
+ return contains("cCxXyYz");
+ }
+ if (modifier == CharT{'O'}) {
+ return contains("deHImMSuUVwWyz");
+ }
+ return false;
+}
+
+template <typename CharT>
+void AppendChronoField(std::basic_string<CharT>* out, FormatArgument argument,
+ CharT specifier, CharT modifier = CharT{}) {
+ *out += {CharT{'{'}, static_cast<CharT>(argument), CharT{':'}, CharT{'L'},
CharT{'%'}};
+ if (modifier != CharT{}) out->push_back(modifier);
+ *out += {specifier, CharT{'}'}};
+}
+
+template <typename CharT>
+void AppendLocalizedField(std::basic_string<CharT>* out, FormatArgument
argument) {
+ *out += {CharT{'{'}, static_cast<CharT>(argument), CharT{':'}, CharT{'L'},
CharT{'}'}};
+}
+
+template <typename CharT>
+std::basic_string<CharT> ToChronoFormat(const CharT* fmt, bool
use_microseconds_suffix) {
+ std::basic_string<CharT> out;
+ while (*fmt != CharT{}) {
+ if (*fmt != CharT{'%'}) {
+ AppendEscapedLiteral(&out, *fmt++);
+ continue;
+ }
+
+ ++fmt;
+ if (*fmt == CharT{}) {
+ AppendEscapedLiteral(&out, CharT{'%'});
+ break;
+ }
+
+ CharT modifier{};
+ if (*fmt == CharT{'E'} || *fmt == CharT{'O'}) {
+ modifier = *fmt++;
+ if (*fmt == CharT{}) {
+ AppendEscapedLiteral(&out, CharT{'%'});
+ AppendEscapedLiteral(&out, modifier);
+ break;
+ }
+ }
+ const CharT specifier = *fmt++;
+
+ if (modifier == CharT{}) {
+ switch (specifier) {
+ case CharT{'%'}:
+ AppendEscapedLiteral(&out, CharT{'%'});
+ continue;
+ case CharT{'n'}:
+ AppendEscapedLiteral(&out, CharT{'\n'});
+ continue;
+ case CharT{'t'}:
+ AppendEscapedLiteral(&out, CharT{'\t'});
+ continue;
+ case CharT{'Q'}:
+ // Formatting a duration's %Q does not consistently apply the
numeric locale.
+ AppendLocalizedField(&out, FormatArgument::TimeOfDayCount);
+ continue;
+ case CharT{'q'}:
+ if (use_microseconds_suffix) {
+ // Some standard libraries use "us"; Arrow uses the micro sign.
+ if constexpr (std::is_same_v<CharT, char>) {
+ AppendEscapedLiteral(&out, CharT{'\xC2'});
+ AppendEscapedLiteral(&out, CharT{'\xB5'});
+ } else {
+ AppendEscapedLiteral(&out, static_cast<CharT>(0xB5));
+ }
+ AppendEscapedLiteral(&out, CharT{'s'});
+ } else {
+ AppendChronoField(&out, FormatArgument::TimeOfDay, specifier);
+ }
+ continue;
+ default:
+ break;
+ }
+ }
+
+# if defined(__GLIBCXX__)
+ if (modifier == CharT{'O'} && specifier == CharT{'V'}) {
+ // libstdc++ does not yet accept %OV; use its equivalent base
representation.
+ AppendChronoField(&out, FormatArgument::ZonedTime, specifier);
+ continue;
+ }
+# endif
+
+ if (IsSupportedStrftimeSpecifier(modifier, specifier)) {
+ AppendChronoField(&out, FormatArgument::ZonedTime, specifier, modifier);
+ } else {
+ AppendEscapedLiteral(&out, CharT{'%'});
+ if (modifier != CharT{}) AppendEscapedLiteral(&out, modifier);
+ AppendEscapedLiteral(&out, specifier);
+ }
+ }
+ return out;
+}
+
+} // namespace detail
+
+// Convert Arrow's strftime syntax to C++20 replacement fields. Literal braces
and
+// unsupported directives remain literal, and %Q/%q use local time of day.
template <typename CharT, typename Traits, typename Duration, typename
TimeZonePtr>
std::basic_ostream<CharT, Traits>& to_stream(
std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
const std::chrono::zoned_time<Duration, TimeZonePtr>& zt) {
- std::vformat_to(std::ostreambuf_iterator<CharT>(os), std::string("{:") + fmt
+ "}",
- std::make_format_args(zt));
+ static_assert(std::is_same_v<CharT, char> || std::is_same_v<CharT, wchar_t>);
+ using Precision = typename std::chrono::zoned_time<Duration,
TimeZonePtr>::duration;
+ const auto standard_format = detail::ToChronoFormat(
+ fmt, std::ratio_equal_v<typename Precision::period, std::micro>);
Review Comment:
This was also moved to `kernels/temporal_internal.h`.
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