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Implement LWG-3956 chrono::parse uses from_stream as a customization point #5334

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Merged
merged 3 commits into from
Mar 13, 2025
+63 −6
Merged

Implement LWG-3956 chrono::parse uses from_stream as a customization point #5334

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10a4e29
Implement LWG-3956
frederick-vs-ja Mar 12, 2025
b27bd2f
Fix copy-pasta
frederick-vs-ja Mar 12, 2025
850fc92
Include `<istream>` for `basic_istream`.
StephanTLavavej Mar 12, 2025
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24 changes: 18 additions & 6 deletions stl/inc/chrono
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Original file line number Diff line number Diff line change
Expand Up @@ -4608,6 +4608,22 @@ namespace chrono {
return _Istr;
}

namespace _From_stream_adl_only {
#if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-1681199
void from_stream() = delete; // Block unqualified name lookup
#else // ^^^ no workaround / workaround vvv
void from_stream();
#endif // ^^^ workaorund ^^^

template <class _Parsable, class _CharT, class _Traits, class... _Rest>
concept _Can_from_stream = requires(
basic_istream<_CharT, _Traits>& __istr, const _CharT* __s, _Parsable& __parsed, _Rest&&... __rest_args) {
from_stream(__istr, +__s, __parsed, _STD forward<_Rest>(__rest_args)...); // intentional ADL
}
} // namespace _From_stream_adl_only

using _From_stream_adl_only::_Can_from_stream;

template <class _CharT, class _Traits, class _Alloc, class _Parsable>
struct _Time_parse_iomanip_c_str {
_Time_parse_iomanip_c_str(const _CharT* _Fmt_, _Parsable& _Tp_,
Expand All @@ -4618,6 +4634,7 @@ namespace chrono {

friend basic_istream<_CharT, _Traits>& operator>>(
basic_istream<_CharT, _Traits>& _Is, _Time_parse_iomanip_c_str&& _Tpi) {
using _From_stream_adl_only::from_stream;
from_stream(_Is, _Tpi._Fmt, _Tpi._Tp, _Tpi._Abbrev, _Tpi._Offset); // intentional ADL
return _Is;
}
Expand All @@ -4638,6 +4655,7 @@ namespace chrono {

friend basic_istream<_CharT, _Traits>& operator>>(
basic_istream<_CharT, _Traits>& _Is, _Time_parse_iomanip&& _Tpi) {
using _From_stream_adl_only::from_stream;
from_stream(_Is, _Tpi._Fmt.c_str(), _Tpi._Tp, _Tpi._Abbrev, _Tpi._Offset); // intentional ADL
return _Is;
}
Expand All @@ -4648,12 +4666,6 @@ namespace chrono {
minutes* _Offset;
};

template <class _Parsable, class _CharT, class _Traits, class... _Rest>
concept _Can_from_stream = requires(
basic_istream<_CharT, _Traits>& __istr, const _CharT* __s, _Parsable& __parsed, _Rest&&... __rest_args) {
from_stream(__istr, +__s, __parsed, _STD forward<_Rest>(__rest_args)...); // intentional ADL
};

_EXPORT_STD template <class _CharT, _Can_from_stream<_CharT, char_traits<_CharT>> _Parsable>
_NODISCARD auto parse(const _CharT* _Fmt, _Parsable& _Tp) {
return _Time_parse_iomanip_c_str<_CharT, char_traits<_CharT>, allocator<_CharT>, _Parsable>{_Fmt, _Tp};
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44 changes: 44 additions & 0 deletions tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
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Expand Up @@ -1247,8 +1247,52 @@ void test_io_manipulator() {
fail_parse(WIDEN(CharT, "a b"), CStringOrStdString{WIDEN(CharT, "a%nb")}, time);
}

namespace lwg_3956 {
struct has_adl_from_stream {
int value = 0;

template <class CharT, class Traits, class... ArgTypes>
friend basic_istream<CharT, Traits>& from_stream(
basic_istream<CharT, Traits>& istr, const CharT*, has_adl_from_stream& parsed, ArgTypes&&...) {
parsed.value = 42;
return istr;
}
};

struct has_no_adl_from_stream {
operator year&() &;
};

template <class... ArgTypes>
concept can_parse = requires(ArgTypes&&... args) { parse(forward<ArgTypes>(args)...); };

static_assert(can_parse<const char*, has_adl_from_stream&>);
static_assert(can_parse<const string&, has_adl_from_stream&>);
static_assert(can_parse<const wchar_t*, has_adl_from_stream&>);
static_assert(can_parse<const wstring&, has_adl_from_stream&>);

static_assert(!can_parse<const char*, has_no_adl_from_stream&>);
static_assert(!can_parse<const string&, has_no_adl_from_stream&>);
static_assert(!can_parse<const wchar_t*, has_no_adl_from_stream&>);
static_assert(!can_parse<const wstring&, has_no_adl_from_stream&>);
} // namespace lwg_3956

void test_lwg_3956() {
{
lwg_3956::has_adl_from_stream parsed{};
test_parse("", "", parsed);
assert(parsed.value == 42);
}
{
lwg_3956::has_adl_from_stream parsed{};
test_parse(L"", L"", parsed);
assert(parsed.value == 42);
}
}

void test_parse() {
test_lwg_3536();
test_lwg_3956();
parse_seconds();
parse_minutes();
parse_hours();
Expand Down
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