From a5a7b68b762242022b75b4c816a6501aae112990 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Fri, 19 Jun 2015 17:25:13 +0200
Subject: [PATCH] Fix ambiguous instanciation using clean class-level SFINAE in
 product_evaluator

---
 Eigen/src/Core/ProductEvaluators.h        | 4 ++--
 Eigen/src/Core/util/ForwardDeclarations.h | 6 +++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Eigen/src/Core/ProductEvaluators.h b/Eigen/src/Core/ProductEvaluators.h
index ee87da66d..2f199bc29 100644
--- a/Eigen/src/Core/ProductEvaluators.h
+++ b/Eigen/src/Core/ProductEvaluators.h
@@ -100,8 +100,8 @@ struct evaluator_traits<Product<Lhs, Rhs, AliasFreeProduct> >
 // This is the default evaluator implementation for products:
 // It creates a temporary and call generic_product_impl
 template<typename Lhs, typename Rhs, int Options, int ProductTag, typename LhsShape, typename RhsShape>
-struct product_evaluator<Product<Lhs, Rhs, Options>, ProductTag, LhsShape, RhsShape, typename traits<Lhs>::Scalar,
-  typename enable_if<(Options==DefaultProduct || Options==AliasFreeProduct),typename traits<Rhs>::Scalar>::type> 
+struct product_evaluator<Product<Lhs, Rhs, Options>, ProductTag, LhsShape, RhsShape, typename traits<Lhs>::Scalar, typename traits<Rhs>::Scalar,
+  EnableIf<(Options==DefaultProduct || Options==AliasFreeProduct)> >
   : public evaluator<typename Product<Lhs, Rhs, Options>::PlainObject>::type
 {
   typedef Product<Lhs, Rhs, Options> XprType;
diff --git a/Eigen/src/Core/util/ForwardDeclarations.h b/Eigen/src/Core/util/ForwardDeclarations.h
index c287c1023..ba75d25af 100644
--- a/Eigen/src/Core/util/ForwardDeclarations.h
+++ b/Eigen/src/Core/util/ForwardDeclarations.h
@@ -147,6 +147,9 @@ template<typename _Scalar, int Rows=Dynamic, int Cols=Dynamic, int Supers=Dynami
 
 namespace internal {
 template<typename Lhs, typename Rhs> struct product_type;
+
+template<bool> struct EnableIf;
+
 /** \internal
   * \class product_evaluator
   * Products need their own evaluator with more template arguments allowing for
@@ -157,7 +160,8 @@ template< typename T,
           typename LhsShape = typename evaluator_traits<typename T::Lhs>::Shape,
           typename RhsShape = typename evaluator_traits<typename T::Rhs>::Shape,
           typename LhsScalar = typename traits<typename T::Lhs>::Scalar,
-          typename RhsScalar = typename traits<typename T::Rhs>::Scalar
+          typename RhsScalar = typename traits<typename T::Rhs>::Scalar,
+          typename = EnableIf<true> // extra template parameter for SFINAE-based specialization
         > struct product_evaluator;
 }