[Bug libstdc++/87194] New: Associative container cannot be inserted from move iterators that refer to elements implicitly convertible to value_type

[kariya_mitsuru at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87194

            Bug ID: 87194
           Summary: Associative container cannot be inserted from move
                    iterators that refer to elements implicitly
                    convertible to value_type
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kariya_mitsuru at hotmail dot com
  Target Milestone: ---

The sample code below is failed to compile by GCC HEAD (Sep 1, 2018).

=========================== sample code ===========================
#include <array>
#include <iterator>
#include <set>
#include <string>
#include <utility>

struct S {
  S(const char* s) : s(s) {}
  operator std::string() && { return std::move(s); }
  std::string s;
};

int main()
{
  std::array<S, 3> a{ "abc", "def", "ghi" };
  std::set<std::string> s;
  s.insert(std::make_move_iterator(a.begin()),
std::make_move_iterator(a.end()));
}
=========================== sample code ===========================
cf. https://wandbox.org/permlink/c8rASYAgPKxRBUt0


The C++17 standard [associative.reqmts] says,

p.8: ..., i and j satisfy input iterator requirements and refer to elements
implicitly convertible to value_type, ...

a.insert(i,j) in Table 90: Requires: value_type shall be EmplaceConstructible
into X from *i.

So, I think that the sample code should be coumpiled successfully.


The unordered_set has the same problem.
cf. https://wandbox.org/permlink/Q4pVJkFVSS2Qijrg

But I don't know why, [unord.req] says that

p.8: ..., i and j denote input iterators that refer to value_type, ...

So, I am not sure that the unordered_set should be too.