1 files changed, 5 insertions, 4 deletions
diff --git a/impl/Variable.hpp b/impl/Variable.hpp
index 0ba13e9..2386e7a 100644
--- a/impl/Variable.hpp
+++ b/impl/Variable.hpp
@@ -5,18 +5,19 @@
 
 template<typename T>
 struct Variable : public Operator<T> {
+  Variable(unsigned int id)
+    : _id(id) { }
+  Variable(const Variable& other)
+    : _id(other._id) { }
   unsigned int id() const {
     return _id;
   }
-  unsigned int id(unsigned int id) {
-    return (_id = id);
-  }
   T operator() (const std::vector< Expression<T>* >& args, const VariableAssignment<T>& ass) const {
     //assert(args.size() == 0)
     return ass[*this];
   }
   private:
-  unsigned int _id;
+  const unsigned int _id;
 };
 
 #endif