Recover compile-time size from seq(A,B) when A and B are fixed values. (c++11 only)

Eigen/src/Core/util/IntegralConstant.h

@@ -28,6 +28,10 @@ template<int N> struct fix_t {
   }
 
   fix_t<-N> operator-() const { return fix_t<-N>(); }
+  template<int M>
+  fix_t<N+M> operator+(fix_t<M>) const { return fix_t<N+M>(); }
+  template<int M>
+  fix_t<N-M> operator-(fix_t<M>) const { return fix_t<N-M>(); }
 
 #if EIGEN_HAS_CXX14
   // Needed in C++14 to allow fix<N>():

Eigen/src/Core/util/SymbolicIndex.h

@@ -163,6 +163,13 @@ struct is_symbolic {
   enum { value = internal::is_convertible<T,BaseExpr<T> >::value };
 };
 
+// Specialization for functions, because is_convertible fails in this case.
+// Useful in c++98/11 mode when testing is_symbolic<decltype(fix<N>)>
+template<typename T>
+struct is_symbolic<T (*)()> {
+  enum { value = false };
+};
+
 /** Represents the actual value of a symbol identified by its tag
   *
   * It is the return type of SymbolValue::operator=, and most of the time this is only way it is used.