From bdfe294e61ff9442495a56c89d1050cdbab8601f Mon Sep 17 00:00:00 2001
From: Christian Mazakas <christian.mazakas@gmail.com>
Date: Mon, 3 Oct 2022 14:47:41 -0700
Subject: [PATCH] Add temporary polyfill for foa table's assignment operator so
 that the definition of the allocator copy-assignment operator isn't required

---
 include/boost/unordered/detail/foa.hpp | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/boost/unordered/detail/foa.hpp b/include/boost/unordered/detail/foa.hpp
index 7f3b7dde..1ea4b3e0 100644
--- a/include/boost/unordered/detail/foa.hpp
+++ b/include/boost/unordered/detail/foa.hpp
@@ -975,16 +975,31 @@ public:
     delete_arrays(arrays);
   }
 
+  template <class AllocTraits>
+  typename std::enable_if<
+    !AllocTraits::propagate_on_container_copy_assignment::value, 
+    void
+  >::type 
+  copy_assign_helper(const table&) {}
+
+  template <class AllocTraits>
+  typename std::enable_if<
+    AllocTraits::propagate_on_container_copy_assignment::value, 
+    void
+  >::type
+  copy_assign_helper(const table& x)
+  {
+    if(al()!=x.al())reserve(0);
+    al()=x.al();
+  }
+
   table& operator=(const table& x)
   {
     if(this!=&x){
       clear();
       h()=x.h();
       pred()=x.pred();
-      if(alloc_traits::propagate_on_container_copy_assignment::value){
-        if(al()!=x.al())reserve(0);
-        al()=x.al();
-      }
+      copy_assign_helper<alloc_traits>(x);
       // TODO may shrink arrays and miss an opportunity for memory reuse
       reserve(x.size());
       x.for_all_elements([this](value_type* p){