Fix incorrect use of reference-to-pointer in Iteration operators

libwccl/ops/functions/bool/iteration.h

@@ -24,10 +24,10 @@ public:
 	std::string to_string(const Corpus2::Tagset& tagset) const;
 
 protected:
-	const PosFunctionPtr& left_pos_expr_;
-	const PosFunctionPtr& right_pos_expr_;
+	const PosFunctionPtr left_pos_expr_;
+	const PosFunctionPtr right_pos_expr_;
 	const VariableAccessor<Position> iter_var_acc_;
-	const BoolFunctionPtr& evaluating_expr_;
+	const BoolFunctionPtr evaluating_expr_;
 	
 	Iteration(
 		const PosFunctionPtr& left_pos_expr,