http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56112
Bug #: 56112
Summary: [4.8 Regression] cannot create unordered_map from
range of types convertible to value_type
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: r...@gcc.gnu.org
#include <unordered_map>
struct S
{
operator std::pair<const int, int>() const { return {}; }
};
int main()
{
S s[1];
std::unordered_map<int, int> m(s, s+1); // error
std::pair<const int, int> p = *s; // OK
m.insert(s, s+1); // OK
}
This is valid (value_type is EmplaceConstructible into the container from s[0])
but it fails to compile because of the change to use std::__detail::_Select1st
instead of std::_Select1st<value_type>
The template argument for _Select1st::operator() cannot be deduced from the
object of type S. The problem boils down to this:
#include <utility>
struct S
{
operator std::pair<const int, int>() const { return {}; }
};
void f()
{
S s;
std::get<0>(s);
}
This is not valid, but the range constructors of unordered_map and
unordered_multimap assume using std::get<0> on the iterator's value type will
work, which is not a valid assumption.
