diff --git a/xs/src/ExtrusionEntity.cpp b/xs/src/ExtrusionEntity.cpp
index eb3507df0..974e8910f 100644
--- a/xs/src/ExtrusionEntity.cpp
+++ b/xs/src/ExtrusionEntity.cpp
@@ -33,7 +33,7 @@ ExtrusionLoop::clone() const
 }
 
 ExtrusionPath*
-ExtrusionLoop::split_at_index(int index)
+ExtrusionLoop::split_at_index(int index) const
 {
     Polyline* poly = this->polygon.split_at_index(index);
     
@@ -48,7 +48,7 @@ ExtrusionLoop::split_at_index(int index)
 }
 
 ExtrusionPath*
-ExtrusionLoop::split_at_first_point()
+ExtrusionLoop::split_at_first_point() const
 {
     return this->split_at_index(0);
 }
diff --git a/xs/src/ExtrusionEntity.hpp b/xs/src/ExtrusionEntity.hpp
index 129115460..c9dd6b080 100644
--- a/xs/src/ExtrusionEntity.hpp
+++ b/xs/src/ExtrusionEntity.hpp
@@ -52,8 +52,8 @@ class ExtrusionLoop : public ExtrusionEntity
     public:
     ExtrusionLoop* clone() const;
     Polygon polygon;
-    ExtrusionPath* split_at_index(int index);
-    ExtrusionPath* split_at_first_point();
+    ExtrusionPath* split_at_index(int index) const;
+    ExtrusionPath* split_at_first_point() const;
     bool make_counter_clockwise();
     void reverse();
     Point* first_point() const;
diff --git a/xs/src/Polygon.cpp b/xs/src/Polygon.cpp
index 9ea5c9104..4132a9fba 100644
--- a/xs/src/Polygon.cpp
+++ b/xs/src/Polygon.cpp
@@ -15,40 +15,40 @@ Lines
 Polygon::lines() const
 {
     Lines lines;
-    for (int i = 0; i < this->points.size()-1; i++) {
-        lines.push_back(Line(this->points[i], this->points[i+1]));
+    lines.reserve(this->points.size());
+    for (Points::const_iterator it = this->points.begin(); it != this->points.end()-1; ++it) {
+        lines.push_back(Line(*it, *(it + 1)));
     }
     lines.push_back(Line(this->points.back(), this->points.front()));
     return lines;
 }
 
 Polyline*
-Polygon::split_at(const Point* point)
+Polygon::split_at(const Point* point) const
 {
     // find index of point
     for (Points::const_iterator it = this->points.begin(); it != this->points.end(); ++it) {
-        if ((*it).coincides_with(point)) {
+        if (it->coincides_with(point))
             return this->split_at_index(it - this->points.begin());
-        }
     }
-    throw "Point not found";
+    CONFESS("Point not found");
+    return NULL;
 }
 
 Polyline*
-Polygon::split_at_index(int index)
+Polygon::split_at_index(int index) const
 {
     Polyline* poly = new Polyline;
-    for (int i = index; i < this->points.size(); i++) {
-        poly->points.push_back( this->points[i] );
-    }
-    for (int i = 0; i <= index; i++) {
-        poly->points.push_back( this->points[i] );
-    }
+    poly->points.reserve(this->points.size() + 1);
+    for (Points::const_iterator it = this->points.begin() + index; it != this->points.end(); ++it)
+        poly->points.push_back(*it);
+    for (Points::const_iterator it = this->points.begin(); it != this->points.begin() + index + 1; ++it)
+        poly->points.push_back(*it);
     return poly;
 }
 
 Polyline*
-Polygon::split_at_first_point()
+Polygon::split_at_first_point() const
 {
     return this->split_at_index(0);
 }
diff --git a/xs/src/Polygon.hpp b/xs/src/Polygon.hpp
index 3855ddc0a..ce8beafb1 100644
--- a/xs/src/Polygon.hpp
+++ b/xs/src/Polygon.hpp
@@ -13,9 +13,9 @@ class Polygon : public MultiPoint {
     public:
     Point* last_point() const;
     Lines lines() const;
-    Polyline* split_at(const Point* point);
-    Polyline* split_at_index(int index);
-    Polyline* split_at_first_point();
+    Polyline* split_at(const Point* point) const;
+    Polyline* split_at_index(int index) const;
+    Polyline* split_at_first_point() const;
     double area() const;
     bool is_counter_clockwise() const;
     bool is_clockwise() const;
diff --git a/xs/src/Polyline.cpp b/xs/src/Polyline.cpp
index 71bb9db56..3046f6b47 100644
--- a/xs/src/Polyline.cpp
+++ b/xs/src/Polyline.cpp
@@ -8,13 +8,15 @@ Polyline::last_point() const
     return new Point(this->points.back());
 }
 
-void
-Polyline::lines(Lines &lines) const
+Lines
+Polyline::lines() const
 {
-    lines.clear();
-    for (int i = 0; i < this->points.size()-1; i++) {
-        lines.push_back(Line(this->points[i], this->points[i+1]));
+    Lines lines;
+    lines.reserve(this->points.size() - 1);
+    for (Points::const_iterator it = this->points.begin(); it != this->points.end()-1; ++it) {
+        lines.push_back(Line(*it, *(it + 1)));
     }
+    return lines;
 }
 
 #ifdef SLIC3RXS
diff --git a/xs/src/Polyline.hpp b/xs/src/Polyline.hpp
index 0658e064f..5ec702726 100644
--- a/xs/src/Polyline.hpp
+++ b/xs/src/Polyline.hpp
@@ -9,7 +9,7 @@ namespace Slic3r {
 class Polyline : public MultiPoint {
     public:
     Point* last_point() const;
-    void lines(Lines &lines) const;
+    Lines lines() const;
     
     #ifdef SLIC3RXS
     SV* to_SV_ref();
diff --git a/xs/xsp/ExtrusionPath.xsp b/xs/xsp/ExtrusionPath.xsp
index 34c845707..db2db16ad 100644
--- a/xs/xsp/ExtrusionPath.xsp
+++ b/xs/xsp/ExtrusionPath.xsp
@@ -15,7 +15,7 @@
         %code{% THIS->polyline.points.pop_back(); %};
     void reverse();
     Lines lines()
-        %code{% RETVAL = Lines(); THIS->polyline.lines(RETVAL); %};
+        %code{% RETVAL = THIS->polyline.lines(); %};
     Point* first_point()
         %code{% const char* CLASS = "Slic3r::Point"; RETVAL = THIS->first_point(); %};
     Point* last_point()
diff --git a/xs/xsp/Polyline.xsp b/xs/xsp/Polyline.xsp
index 15ee0c5ff..3f681f3cb 100644
--- a/xs/xsp/Polyline.xsp
+++ b/xs/xsp/Polyline.xsp
@@ -18,8 +18,7 @@
     void pop_back()
         %code{% THIS->points.pop_back(); %};
     void reverse();
-    Lines lines()
-        %code{% RETVAL = Lines(); THIS->lines(RETVAL); %};
+    Lines lines();
     Point* first_point()
         %code{% const char* CLASS = "Slic3r::Point"; RETVAL = THIS->first_point(); %};
     Point* last_point()