From d5e5c08b875e1d4ef2e0bd1354ebfd8e218fd2d7 Mon Sep 17 00:00:00 2001
From: Christian Mazakas <christian.mazakas@gmail.com>
Date: Mon, 3 Jan 2022 14:43:51 -0800
Subject: [PATCH] Implement heterogeneous `count()` for multiset

---
 include/boost/unordered/unordered_set.hpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/boost/unordered/unordered_set.hpp b/include/boost/unordered/unordered_set.hpp
index 81f6e2f4..92ab11c5 100644
--- a/include/boost/unordered/unordered_set.hpp
+++ b/include/boost/unordered/unordered_set.hpp
@@ -1092,6 +1092,18 @@ namespace boost {
 
       size_type count(const key_type&) const;
 
+      template <class Key>
+      typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
+        size_type>::type
+      count(const Key& k) const
+      {
+        node_pointer n = table_.find_node_impl(
+          table::policy::apply_hash(this->hash_function(), k), k,
+          this->key_eq());
+
+        return n ? table_.group_count(n) : 0;
+      }
+
       std::pair<const_iterator, const_iterator> equal_range(
         const key_type&) const;