Add operators to make points sortable

The order is more or less arbitrary. This is only so that there is some
kind of order for comparing sets of points etc.

Author: joto

src/geom.hpp

@@ -84,6 +84,23 @@ class point_t
         return !(a == b);
     }
 
+    /// Give points an (arbitrary) order.
+    [[nodiscard]] constexpr friend bool operator<(point_t a, point_t b) noexcept
+    {
+        if (a.x() == b.x()) {
+            return a.y() < b.y();
+        }
+        return a.x() < b.x();
+    }
+
+    [[nodiscard]] constexpr friend bool operator>(point_t a, point_t b) noexcept
+    {
+        if (a.x() == b.x()) {
+            return a.y() > b.y();
+        }
+        return a.x() > b.x();
+    }
+
 private:
     double m_x = 0.0;
     double m_y = 0.0;

tests/test-geom-points.cpp

@@ -61,6 +61,24 @@ TEST_CASE("create_point from OSM data", "[NoDB]")
     REQUIRE(geom.get<geom::point_t>() == geom::point_t{1.1, 2.2});
 }
 
+TEST_CASE("point order", "[NoDB]")
+{
+    geom::point_t const p{10, 10};
+    REQUIRE_FALSE(p < p);
+    REQUIRE_FALSE(p > p);
+
+    std::vector<geom::point_t> points = {
+        {10, 10}, {20, 10}, {13, 14}, {13, 10}
+    };
+
+    std::sort(points.begin(), points.end());
+
+    REQUIRE(points[0] == geom::point_t(10, 10));
+    REQUIRE(points[1] == geom::point_t(13, 10));
+    REQUIRE(points[2] == geom::point_t(13, 14));
+    REQUIRE(points[3] == geom::point_t(20, 10));
+}
+
 TEST_CASE("geom::distance", "[NoDB]")
 {
     geom::point_t const p1{10, 10};