From 6ba13aa25e31065cc6cb5efed1210455217ea379 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 7 Apr 2021 12:53:19 +1000
Subject: [PATCH] introspection/name: add member_offset query for
 pointer-to-member

---
 introspection/name.hpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/introspection/name.hpp b/introspection/name.hpp
index 36b192f2..024a9bf8 100644
--- a/introspection/name.hpp
+++ b/introspection/name.hpp
@@ -168,6 +168,15 @@ namespace cruft::introspection::name {
     }
 
 
+    constexpr std::size_t
+    member_offset (auto ptr)
+    {
+        using klass_t = typename pointer_to_member_class<decltype (ptr)>::type;
+        klass_t instance {};
+        return std::uintptr_t (&(instance.*ptr)) - std::uintptr_t (&instance);
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     template <typename T>
     struct type_char;