From e32dfafbae37ff995f165f7195eb847eaf60254d Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Sat, 15 Aug 2015 13:15:44 +0300
Subject: [PATCH] First stab at fixing #55

---
 libuavcan/include/uavcan/marshal/array.hpp  | 11 +++++++++--
 libuavcan/include/uavcan/util/templates.hpp | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/libuavcan/include/uavcan/marshal/array.hpp b/libuavcan/include/uavcan/marshal/array.hpp
index 9a51fb131e..3f112e4ce5 100644
--- a/libuavcan/include/uavcan/marshal/array.hpp
+++ b/libuavcan/include/uavcan/marshal/array.hpp
@@ -1085,16 +1085,23 @@ public:
     typedef SizeType size_type;
 };
 
+/**
+ * These operators will only be enabled if rhs and lhs are different types. This precondition allows to work-around
+ * the ambiguity arising from the scope containing two definitions: one here and the others in Array<>.
+ * Refer to https://github.com/UAVCAN/libuavcan/issues/55 for more info.
+ */
 template <typename R, typename T, ArrayMode ArrayMode, unsigned MaxSize>
 UAVCAN_EXPORT
-inline bool operator==(const R& rhs, const Array<T, ArrayMode, MaxSize>& lhs)
+inline typename EnableIf<!IsSameType<R, Array<T, ArrayMode, MaxSize> >::Result, bool>::Type
+operator==(const R& rhs, const Array<T, ArrayMode, MaxSize>& lhs)
 {
     return lhs.operator==(rhs);
 }
 
 template <typename R, typename T, ArrayMode ArrayMode, unsigned MaxSize>
 UAVCAN_EXPORT
-inline bool operator!=(const R& rhs, const Array<T, ArrayMode, MaxSize>& lhs)
+inline typename EnableIf<!IsSameType<R, Array<T, ArrayMode, MaxSize> >::Result, bool>::Type
+operator!=(const R& rhs, const Array<T, ArrayMode, MaxSize>& lhs)
 {
     return lhs.operator!=(rhs);
 }
diff --git a/libuavcan/include/uavcan/util/templates.hpp b/libuavcan/include/uavcan/util/templates.hpp
index 9358a73f36..f842d4035f 100644
--- a/libuavcan/include/uavcan/util/templates.hpp
+++ b/libuavcan/include/uavcan/util/templates.hpp
@@ -91,6 +91,21 @@ struct UAVCAN_EXPORT Select<false, TrueType, FalseType>
     typedef FalseType Result;
 };
 
+/**
+ * Checks if two identifiers refer to the same type.
+ */
+template<class T, class U>
+struct IsSameType
+{
+    enum { Result = 0 };
+};
+
+template <typename T>
+struct IsSameType<T, T>
+{
+    enum { Result = 1 };
+};
+
 /**
  * Remove reference as in <type_traits>
  */