Change return type of along to Feature<Point> (#161)

This goes along with preferring to pass around full Features,
and it allow to in the future set properties on the returned
point without it being a breaking change.

lib/src/along.dart

@@ -14,7 +14,7 @@ import 'package:turf/src/invariant.dart';
 ///   the start point of the line is returned.
 /// If [distance] is larger than line length, the end point is returned
 /// If [line] have no geometry or coordinates, an Exception is thrown
-Point along(Feature<LineString> line, num distance,
+Feature<Point> along(Feature<LineString> line, num distance,
     [Unit unit = Unit.kilometers]) {
   // Get Coords
   final coords = getCoords(line);
@@ -30,7 +30,7 @@ Point along(Feature<LineString> line, num distance,
       break;
     }
     if (travelled == distance) {
-      return Point(coordinates: coords[i]);
+      return Feature<Point>(geometry: Point(coordinates: coords[i]));
     }
     if (travelled > distance) {
       final overshot = distance - travelled;
@@ -43,11 +43,12 @@ Point along(Feature<LineString> line, num distance,
         direction,
         unit,
       );
-      return interpolated;
+      return Feature<Point>(geometry: interpolated);
     } else {
       travelled += measure_distance.distance(Point(coordinates: coords[i]),
           Point(coordinates: coords[i + 1]), unit);
     }
   }
-  return Point(coordinates: coords[coords.length - 1]);
+  return Feature<Point>(
+      geometry: Point(coordinates: coords[coords.length - 1]));
 }

test/components/along_test.dart

@@ -10,28 +10,32 @@ void main() {
         distance(Point(coordinates: via), Point(coordinates: end), Unit.meters);
     expect(viaToEndDistance.round(), equals(198));
     final resolvedViaPoint = along(line, -1 * viaToEndDistance, Unit.meters);
-    expect(resolvedViaPoint.coordinates, equals(via));
+    expect(resolvedViaPoint.geometry, isNotNull);
+    expect(resolvedViaPoint.geometry!.coordinates, equals(via));
   });
   test('along - to start point', () {
     final resolvedStartPoint = along(line, 0, Unit.meters);
-    expect(resolvedStartPoint.coordinates, equals(start));
+    expect(resolvedStartPoint.geometry, isNotNull);
+    expect(resolvedStartPoint.geometry!.coordinates, equals(start));
   });
   test('along - to point between start and via', () {
     final startToViaDistance = distance(
         Point(coordinates: start), Point(coordinates: via), Unit.meters);
     expect(startToViaDistance.round(), equals(57));
     final resolvedViaPoint = along(line, startToViaDistance / 2, Unit.meters);
-    expect(resolvedViaPoint.coordinates.lat.toStringAsFixed(6),
+    expect(resolvedViaPoint.geometry, isNotNull);
+    expect(resolvedViaPoint.geometry!.coordinates.lat.toStringAsFixed(6),
         equals('55.709028'));
-    expect(resolvedViaPoint.coordinates.lng.toStringAsFixed(6),
+    expect(resolvedViaPoint.geometry!.coordinates.lng.toStringAsFixed(6),
         equals('13.185096'));
   });
   test('along - to via point', () {
     final startToViaDistance = distance(
         Point(coordinates: start), Point(coordinates: via), Unit.meters);
     expect(startToViaDistance.round(), equals(57));
     final resolvedViaPoint = along(line, startToViaDistance, Unit.meters);
-    expect(resolvedViaPoint.coordinates, equals(via));
+    expect(resolvedViaPoint.geometry, isNotNull);
+    expect(resolvedViaPoint.geometry!.coordinates, equals(via));
   });
   test('along - to point between via and end', () {
     final startToViaDistance = distance(
@@ -42,28 +46,32 @@ void main() {
     expect(viaToEndDistance.round(), equals(198));
     final resolvedViaPoint =
         along(line, startToViaDistance + viaToEndDistance / 2, Unit.meters);
-    expect(resolvedViaPoint.coordinates.lat.toStringAsFixed(6),
+    expect(resolvedViaPoint.geometry, isNotNull);
+    expect(resolvedViaPoint.geometry!.coordinates.lat.toStringAsFixed(6),
         equals('55.708330'));
-    expect(resolvedViaPoint.coordinates.lng.toStringAsFixed(6),
+    expect(resolvedViaPoint.geometry!.coordinates.lng.toStringAsFixed(6),
         equals('13.186555'));
   });
   test('along - to end point', () {
     final len = length(line, Unit.meters);
     expect(len.round(), equals(254));
     final resolvedEndPoint = along(line, len, Unit.meters);
-    expect(resolvedEndPoint.coordinates, equals(end));
+    expect(resolvedEndPoint.geometry, isNotNull);
+    expect(resolvedEndPoint.geometry!.coordinates, equals(end));
   });
   test('along - to end point - default unit (km)', () {
     final len = length(line);
     expect((len * 1000).round(), equals(254));
     final resolvedEndPoint = along(line, len);
-    expect(resolvedEndPoint.coordinates, equals(end));
+    expect(resolvedEndPoint.geometry, isNotNull);
+    expect(resolvedEndPoint.geometry!.coordinates, equals(end));
   });
   test('along - beyond end point', () {
     final len = length(line, Unit.meters);
     expect(len.round(), equals(254));
     final resolvedEndPoint = along(line, len + 100, Unit.meters);
-    expect(resolvedEndPoint.coordinates, equals(end));
+    expect(resolvedEndPoint.geometry, isNotNull);
+    expect(resolvedEndPoint.geometry!.coordinates, equals(end));
   });
 }