From 3945a3add9f8710d56663db2101c017435a50475 Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Wed, 8 Jun 2022 18:27:29 +0200
Subject: [PATCH] util/MemberPointer: new library

---
 src/util/MemberPointer.hxx | 56 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 src/util/MemberPointer.hxx

diff --git a/src/util/MemberPointer.hxx b/src/util/MemberPointer.hxx
new file mode 100644
index 000000000..231a6682e
--- /dev/null
+++ b/src/util/MemberPointer.hxx
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2022 CM4all GmbH
+ * All rights reserved.
+ *
+ * author: Max Kellermann <mk@cm4all.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+template<typename T>
+struct MemberPointerHelper;
+
+template<typename C, typename M>
+struct MemberPointerHelper<M C::*> {
+	using ContainerType = C;
+	using MemberType = M;
+};
+
+/**
+ * Given a member pointer, this determines the member type.
+ */
+template<typename T>
+using MemberPointerType =
+	typename MemberPointerHelper<T>::MemberType;
+
+/**
+ * Given a member pointer, this determines the container type.
+ */
+template<typename T>
+using MemberPointerContainerType =
+	typename MemberPointerHelper<T>::ContainerType;