From ff4d25d45404a8c7983133193909dd2ede761ce7 Mon Sep 17 00:00:00 2001
From: Christian Mazakas <christian.mazakas@gmail.com>
Date: Tue, 21 Dec 2021 09:21:51 -0800
Subject: [PATCH] Add `transparent_non_iterable` type trait for usage in
 `erase()` / `extract()` SFINAE

---
 include/boost/unordered/detail/implementation.hpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/boost/unordered/detail/implementation.hpp b/include/boost/unordered/detail/implementation.hpp
index 23c4314a..935cbb30 100644
--- a/include/boost/unordered/detail/implementation.hpp
+++ b/include/boost/unordered/detail/implementation.hpp
@@ -36,6 +36,7 @@
 #include <boost/type_traits/integral_constant.hpp>
 #include <boost/type_traits/is_base_of.hpp>
 #include <boost/type_traits/is_class.hpp>
+#include <boost/type_traits/is_convertible.hpp>
 #include <boost/type_traits/is_empty.hpp>
 #include <boost/type_traits/is_nothrow_move_assignable.hpp>
 #include <boost/type_traits/is_nothrow_move_constructible.hpp>
@@ -718,6 +719,19 @@ namespace boost {
           is_transparent<A>::value && is_transparent<B>::value;
       };
 
+      template <class Key, class UnorderedMap> struct transparent_non_iterable
+      {
+        typedef typename UnorderedMap::hasher hash;
+        typedef typename UnorderedMap::key_equal key_equal;
+        typedef typename UnorderedMap::iterator iterator;
+        typedef typename UnorderedMap::const_iterator const_iterator;
+
+        static bool const value =
+          are_transparent<Key, hash, key_equal>::value &&
+          !boost::is_convertible<Key, iterator>::value &&
+          !boost::is_convertible<Key, const_iterator>::value;
+      };
+
 ////////////////////////////////////////////////////////////////////////////
 // Explicitly call a destructor