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4499. flat_set::insert_range specification may be problematic

Section: 23.6.11.5 [flat.set.modifiers], 23.6.12.5 [flat.multiset.modifiers] Status: New Submitter: Hewill Kang Opened: 2025-12-22 Last modified: 2025-12-22

Priority: Not Prioritized

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Discussion:

The function adds elements via:

ranges::for_each(rg, [&](auto&& e) {
  c.insert(c.end(), std::forward<decltype(e)>(e));
});

Here, e is an element of the input range.

However, this can lead to ambiguity when e can also be converted to initializer_list, as vector::insert has an overload of insert(const_iterator, initializer_list<T>).

Proposed resolution:

This wording is relative to N5032.

1. Modify 23.6.11.5 [flat.set.modifiers] as indicated:

   template<container-compatible-range<value_type> R>
     constexpr void insert_range(R&& rg);
   

   -10- Effects: Adds elements to c as if by:

   ranges::for_each(rg, [&](value_typeauto&& e) {
     c.insert(c.end(), std::movestd::forward<decltype(e)>(e));
   });
   

2. Modify 23.6.12.5 [flat.multiset.modifiers] as indicated:

   template<container-compatible-range<value_type> R>
     void insert_range(R&& rg);
   

   -9- Effects: Adds elements to c as if by:

   ranges::for_each(rg, [&](value_typeauto&& e) {
     c.insert(c.end(), std::movestd::forward<decltype(e)>(e));
   });