From c79b633a1ca0ad754c6739ea14b6ef8bc5c66aad Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Sun, 29 Jan 2023 21:27:53 -0800
Subject: [PATCH] Use std::pointer_traits::to_address when available

---
 common/almalloc.h | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/common/almalloc.h b/common/almalloc.h
index b73b159b..809f4f1f 100644
--- a/common/almalloc.h
+++ b/common/almalloc.h
@@ -106,6 +106,17 @@ template<typename T, std::size_t N, typename U, std::size_t M>
 constexpr bool operator!=(const allocator<T,N>&, const allocator<U,M>&) noexcept { return false; }
 
 
+namespace detail_ {
+    template<typename... Ts>
+    using void_t = void;
+
+    template<typename T, typename = void>
+    constexpr bool has_to_address = false;
+    template<typename T>
+    constexpr bool has_to_address<T,
+        void_t<decltype(std::pointer_traits<T>::to_address(std::declval<const T&>()))>> = true;
+} // namespace detail_
+
 template<typename T>
 constexpr T *to_address(T *p) noexcept
 {
@@ -113,7 +124,11 @@ constexpr T *to_address(T *p) noexcept
     return p;
 }
 
-template<typename T>
+template<typename T, std::enable_if_t<detail_::has_to_address<T>,bool> = true>
+constexpr auto to_address(const T& p) noexcept
+{ return std::pointer_traits<T>::to_address(p); }
+
+template<typename T, std::enable_if_t<!detail_::has_to_address<T>,bool> = true>
 constexpr auto to_address(const T& p) noexcept
 { return to_address(p.operator->()); }