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<flat_map>: Pass a tinier value_compare-like comparator to algorithms #6038

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 1 commit into from
Jan 22, 2026
Merged

<flat_map>: Pass a tinier value_compare-like comparator to algorithms #6038

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26 changes: 22 additions & 4 deletions stl/inc/flat_map
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Original file line number Diff line number Diff line change
Expand Up @@ -275,6 +275,21 @@ struct _NODISCARD _Flat_map_swap_clear_guard<true, _Containers> {
void _Dismiss() noexcept {}
};

template <class _Compare, class _Key, class _Mapped>
struct _Value_compare_to_pass_in_flat_map {
using _Key_compare =
conditional_t<conjunction_v<bool_constant<sizeof(_Compare) <= sizeof(void*)>,
is_trivially_copy_constructible<_Compare>, is_trivially_destructible<_Compare>>,
_Compare, const _Compare&>;
using _Const_reference = pair<const _Key&, const _Mapped&>;

_Key_compare _Key_comparator;

_NODISCARD bool operator()(_Const_reference _Left, _Const_reference _Right) const {
return _Key_comparator(_Left.first, _Right.first);
}
};

_EXPORT_STD template <class _Key, class _Mapped, class _Compare = less<_Key>, class _KeyContainer = vector<_Key>,
class _MappedContainer = vector<_Mapped>>
class flat_map;
Expand Down Expand Up @@ -1066,6 +1081,8 @@ public:
}

private:
using _Value_compare_to_pass = _Value_compare_to_pass_in_flat_map<_Compare, _Key, _Mapped>;

_NODISCARD bool _Is_sorted_and_unique(
const key_container_type::const_iterator _It, const key_container_type::const_iterator _End) const {
if constexpr (_IsUnique) {
Expand All @@ -1092,8 +1109,8 @@ private:
auto _View = _View_to_mutate();
const auto _Begin_unsorted_values = _View.begin() + _Num_sorted;

_RANGES sort(_Begin_unsorted_values, _View.end(), value_compare{_Key_compare});
_RANGES inplace_merge(_View, _Begin_unsorted_values, value_compare{_Key_compare});
_RANGES sort(_Begin_unsorted_values, _View.end(), _Value_compare_to_pass{_Key_compare});
_RANGES inplace_merge(_View, _Begin_unsorted_values, _Value_compare_to_pass{_Key_compare});

_Erase_dupes_if_not_multi();

Expand Down Expand Up @@ -1146,7 +1163,8 @@ private:
// Sort the newly inserted elements
auto _Sorted_view = _View_to_mutate();
if constexpr (_NeedSorting) {
_RANGES sort(_Sorted_view.begin() + _Old_distance, _Sorted_view.end(), value_compare{_Key_compare});
_RANGES sort(
_Sorted_view.begin() + _Old_distance, _Sorted_view.end(), _Value_compare_to_pass{_Key_compare});
} else {
_STL_ASSERT(_Is_sorted_and_unique(
_Data.keys.begin() + static_cast<key_container_type::difference_type>(_Old_distance),
Expand All @@ -1155,7 +1173,7 @@ private:
}

// Merge the newly inserted elements with the existing elements
_RANGES inplace_merge(_Sorted_view, _Sorted_view.begin() + _Old_distance, value_compare{_Key_compare});
_RANGES inplace_merge(_Sorted_view, _Sorted_view.begin() + _Old_distance, _Value_compare_to_pass{_Key_compare});

_Erase_dupes_if_not_multi();
_STL_INTERNAL_CHECK(_Is_sorted_and_unique());
Expand Down