From b916df3b6208697b7af9c00cbd75cf58c173e228 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emmanuel=20Beno=C3=AEt?= <tseeker@nocternity.net>
Date: Wed, 2 Jan 2019 17:39:55 +0100
Subject: [PATCH] Utilities - EnableForHierarchy< T1 , T2 >

Templated horror that corresponds to a std::enable_if for which the
condition will be true if T1 and T2 are in the same type hierarchy.
---
 include/ebcl/Utilities.hh | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/ebcl/Utilities.hh b/include/ebcl/Utilities.hh
index 875cc1a..86ba32b 100644
--- a/include/ebcl/Utilities.hh
+++ b/include/ebcl/Utilities.hh
@@ -136,8 +136,7 @@ template< typename... List >
 template<
 	typename Parent ,
 	typename Child
->
-using EnableForChild =
+> using EnableForChild =
 	std::enable_if<
 		std::is_base_of< Parent , Child >::value ,
 		bool
@@ -151,8 +150,7 @@ using T_EnableForChild = typename EnableForChild<C, P>::type;
 template<
 	typename Child ,
 	typename Parent
->
-using EnableForParent =
+> using EnableForParent =
 	std::enable_if<
 		std::is_base_of< Parent , Child >::value
 			&& !std::is_same< Parent , Child >::value ,
@@ -162,6 +160,25 @@ using EnableForParent =
 template< typename C , typename P >
 using T_EnableForParent = typename EnableForParent<C, P>::type;
 
+// EnableForHierarchy< T1 , T2 > - Enable if T1 and T2 are the same, or if
+// T1 is the child of T2 or if T2 is the child of T1
+template<
+	typename T1 ,
+	typename T2
+> using EnableForHierarchy =
+	std::enable_if< MetaOr<
+			std::is_same< T1 , T2 > ,
+			std::is_base_of< T1 , T2 > ,
+			std::is_base_of< T2 , T1 >
+		>::value ,
+		bool
+	>;
+
+template<
+	typename T1 ,
+	typename T2
+> using T_EnableForHierarchy = typename EnableForHierarchy< T1 , T2 >::type;
+
 /*----------------------------------------------------------------------------*/
 
 // Remove const and topmost reference