For some reason, the compiler was allowing assignment to these returned locations. That has no effect and is broken, so add const to prevent it.

src/location.cpp

@@ -178,23 +178,23 @@ const rectangle_size_delegate rectangle::height() const {
 	return rectangle_size_delegate(*const_cast<rectangle*>(this), &rectangle::top, &rectangle::bottom);
 }
 
-location rectangle::centre() const {
+const location rectangle::centre() const {
 	return location((left + right) / 2, (top + bottom) / 2);
 }
 
-location rectangle::topLeft() const {
+const location rectangle::topLeft() const {
 	return location(left, top);
 }
 
-location rectangle::topRight() const {
+const location rectangle::topRight() const {
 	return location(right, top);
 }
 
-location rectangle::bottomLeft() const {
+const location rectangle::bottomLeft() const {
 	return location(left, bottom);
 }
 
-location rectangle::bottomRight() const {
+const location rectangle::bottomRight() const {
 	return location(right, bottom);
 }
 
@@ -433,4 +433,4 @@ int closest_point_idx(std::vector<location> points, location anchor) {
 
 location closest_point(std::vector<location> points, location anchor) {
 	return points[closest_point_idx(points, anchor)];
-}
+}

src/location.hpp

@@ -81,11 +81,11 @@ struct rectangle {
 	rectangle_size_delegate height();
 	const rectangle_size_delegate width() const;
 	const rectangle_size_delegate height() const;
-	location centre() const;
-	location topLeft() const;
-	location topRight() const;
-	location bottomLeft() const;
-	location bottomRight() const;
+	const location centre() const;
+	const location topLeft() const;
+	const location topRight() const;
+	const location bottomLeft() const;
+	const location bottomRight() const;
 	bool contains(location p) const;
 	bool contains(int x, int y) const;
 	bool empty() const;