From 0bdb6b8a8a1cb82a89ae36343c8b0ce3cc3c9e52 Mon Sep 17 00:00:00 2001
From: Mathias Agopian <mathias@google.com>
Date: Wed, 30 Jan 2019 14:01:25 -0800
Subject: [PATCH] workaround a compile error with some compilers

---
 libs/utils/include/utils/Allocator.h | 34 ++++++++++++++++------------
 libs/utils/test/test_Allocators.cpp  |  4 ++++
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/libs/utils/include/utils/Allocator.h b/libs/utils/include/utils/Allocator.h
index 68f1836f13..a16a376dcf 100644
--- a/libs/utils/include/utils/Allocator.h
+++ b/libs/utils/include/utils/Allocator.h
@@ -18,17 +18,18 @@
 #define TNT_UTILS_ALLOCATOR_H
 
 
-#include <assert.h>
-#include <stddef.h>
-#include <stdlib.h>
-
-#include <atomic>
-#include <mutex>
-
 #include <utils/compiler.h>
 #include <utils/memalign.h>
 #include <utils/Mutex.h>
 
+#include <atomic>
+#include <mutex>
+#include <type_traits>
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdlib.h>
+
 namespace utils {
 
 namespace pointermath {
@@ -746,17 +747,22 @@ public:
         mArena.free(p, n * sizeof(TYPE));
     }
 
-private:
-    template <typename T, typename U, typename A>
-    friend bool operator==(const STLAllocator<T, A>& rhs, const STLAllocator<U, A>& lhs) {
-        return &rhs.mArena == &lhs.mArena;
+    // these should be out-of-class friends, but this doesn't seem to work with some compilers
+    // which complain about multiple definition each time a STLAllocator<> is instantiated.
+    template <typename U, typename A>
+    bool operator==(const STLAllocator<U, A>& lhs) noexcept {
+        return std::addressof(mArena) == std::addressof(lhs.mArena);
     }
 
-    template <typename T, typename U, typename A>
-    friend bool operator!=(const STLAllocator<T, A>& rhs, const STLAllocator<U, A>& lhs) {
-        return !operator==(rhs, lhs);
+    template <typename U, typename A>
+    bool operator!=(const STLAllocator<U, A>& lhs) noexcept {
+        return !operator==(lhs);
     }
 
+private:
+    template<typename U, typename A>
+    friend class STLAllocator;
+
     ARENA& mArena;
 };
 
diff --git a/libs/utils/test/test_Allocators.cpp b/libs/utils/test/test_Allocators.cpp
index af4fff3ff1..746e6740e1 100644
--- a/libs/utils/test/test_Allocators.cpp
+++ b/libs/utils/test/test_Allocators.cpp
@@ -302,7 +302,11 @@ TEST(AllocatorTest, STLAllocator) {
 
     using Arena = Arena<LinearAllocator, LockingPolicy::NoLock, Tracking>;
     Arena arena("arena", 1204);
+    Arena arena2("arena2", 1204);
     STLAllocator<int, Arena> allocator(arena);
+    STLAllocator<int, Arena> allocator2(arena2);
+    EXPECT_TRUE(allocator != allocator2);
+    EXPECT_TRUE(allocator == allocator);
 
     {
 #if !defined(WIN32)