Because the _M_format(__rg, __fc) were placed outside of if constexpr,
these method and it's childs where instantiated, even if _M_format<const _Range>
could be used.
To simplify the if constexpr chain, we introduce a __simply_formattable_range
(name based on simple-view) exposition only concept, that checks if range is
const and mutable formattable and uses same formatter specialization for
references in each case.
PR libstdc++/109162
libstdc++-v3/ChangeLog:
* include/std/format (__format::__simply_formattable_range): Define.
(range_formatter::format): Do not instantiate _M_format for mutable
_Rg if const _Rg can be used.
Signed-off-by: Tomasz Kamiński <[email protected]>
---
I was really unhappy with repeated ifs, so introduced an helper concept,
that I think is usable in general.
libstdc++-v3/include/std/format | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 27253f50ea8..1780951b61d 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -5252,6 +5252,14 @@ namespace __format
= ranges::input_range<const _Rg>
&& formattable<ranges::range_reference_t<const _Rg>, _CharT>;
+ // _Rg& and const _Rg& are both formttable and use same formatter
+ // specialization for their references.
+ template<typename _Rg, typename _CharT>
+ concept __simply_formattable_range
+ = __const_formattable_range<_Rg, _CharT>
+ && same_as<remove_cvref_t<ranges::range_reference_t<_Rg>>,
+ remove_cvref_t<ranges::range_reference_t<const _Rg>>>;
+
template<typename _Rg, typename _CharT>
using __maybe_const_range
= __conditional_t<__const_formattable_range<_Rg, _CharT>, const _Rg,
_Rg>;
@@ -5635,13 +5643,10 @@ namespace __format
format(_Rg&& __rg, basic_format_context<_Out, _CharT>& __fc) const
{
using _Range = remove_reference_t<_Rg>;
- if constexpr (__format::__const_formattable_range<_Range, _CharT>)
- {
- using _CRef = ranges::range_reference_t<const _Range>;
- if constexpr (same_as<remove_cvref_t<_CRef>, _Tp>)
- return _M_format<const _Range>(__rg, __fc);
- }
- return _M_format(__rg, __fc);
+ if constexpr (__format::__simply_formattable_range<_Range, _CharT>)
+ return _M_format<const _Range>(__rg, __fc);
+ else
+ return _M_format(__rg, __fc);
}
private:
--
2.49.0
