From 012437c57343daef323e06d21d6daa63a5a49202 Mon Sep 17 00:00:00 2001
From: Frank Dellaert <dellaert@gmail.com>
Date: Thu, 3 Sep 2009 17:24:46 +0000
Subject: [PATCH] keys now returns const references

---
 cpp/NonlinearFactor.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cpp/NonlinearFactor.h b/cpp/NonlinearFactor.h
index 7d2b4adbe..229df2285 100644
--- a/cpp/NonlinearFactor.h
+++ b/cpp/NonlinearFactor.h
@@ -65,7 +65,7 @@ namespace gtsam {
     /** get functions */
     double get_sigma() const {return sigma_;}
     Vector get_measurement() const {return z_;}
-    std::list<std::string> get_keys() const {return keys_;}
+    const std::list<std::string>& get_keys() const {return keys_;}
     void set_keys(std::list<std::string> keys) {keys_ = keys;}
 
     /** calculate the error of the factor */