[refactored] distanceFrom to have a shorthand signature

Summary: Part of #230 Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, #material_motion, vietanh Reviewed By: #material_motion, vietanh Subscribers: vietanh Tags: #material_motion Differential Revision: http://codereview.cc/D3422
material-motion · Oct 11, 2017 · ac4f518 · ac4f518
1 parent cb16ebe
commit ac4f518
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Showing 3 changed files with 38 additions and 8 deletions.
diff --git a/packages/core/src/interactions/Swipeable.ts b/packages/core/src/interactions/Swipeable.ts
@@ -174,9 +174,7 @@ export class Swipeable {
     // `resistanceProgress`. Thus, we independently calculate the threshold
     // here.
 
-    this.isThresholdMet$ = draggedX$.distanceFrom({
-      origin$: 0,
-    }).threshold({ limit$: Swipeable.VISUAL_THRESHOLD }).isAnyOf({
+    this.isThresholdMet$ = draggedX$.distanceFrom(0).threshold({ limit$: Swipeable.VISUAL_THRESHOLD }).isAnyOf({
         candidates: [ThresholdRegion.ABOVE, ThresholdRegion.WITHIN]
     });
     this.whenThresholdCrossed$ = when(this.isThresholdMet$.dedupe());

diff --git a/packages/core/src/operators/__tests__/distanceFrom.test.ts b/packages/core/src/operators/__tests__/distanceFrom.test.ts
@@ -87,5 +87,27 @@ describe('motionObservable.distanceFrom',
         expect(valueInLastCall).to.be.closeTo(hypoteneuse, 1);
       }
     );
+
+    it('should accept a shorthand signature for numbers',
+      () => {
+        stream.distanceFrom(10).subscribe(listener);
+
+        mockObserver.next(15);
+
+        expect(listener).to.have.been.calledWith(5);
+      }
+    );
+
+    it('should accept a shorthand signature for points',
+      () => {
+        stream.distanceFrom({ x: 100, y: 100 }).subscribe(listener);
+
+        mockObserver.next({ x: 0, y: 0 });
+
+        const hypoteneuse = 100 / Math.cos(Math.PI / 4);
+        const valueInLastCall = listener.lastCall.args[0];
+        expect(valueInLastCall).to.be.closeTo(hypoteneuse, 1);
+      }
+    );
   }
 );
diff --git a/packages/core/src/operators/distanceFrom.ts b/packages/core/src/operators/distanceFrom.ts
@@ -17,21 +17,25 @@
 import {
   Constructor,
   Dict,
-  MaybeReactive,
   MotionReactiveMappable,
+  Observable,
   ObservableWithMotionOperators,
   Point2D,
 } from '../types';
 
 import {
+  isDefined,
   isPoint2D,
 } from '../typeGuards';
 
-export type DistanceFromArgs<T> = MaybeReactive<{
-  origin$: T & (Point2D | number),
-}>;
+export type DistanceFromOrigin<T> = (T & (Point2D | number)) | Observable<T & (Point2D | number)>;
+
+export type DistanceFromArgs<T> = {
+  origin$: DistanceFromOrigin<T>,
+};
 
 export interface MotionMeasurable<T> {
+  distanceFrom(origin$: DistanceFromOrigin<T>): ObservableWithMotionOperators<number>;
   distanceFrom(kwargs: DistanceFromArgs<T>): ObservableWithMotionOperators<number>;
 }
 
@@ -42,7 +46,13 @@ export function withDistanceFrom<T, S extends Constructor<MotionReactiveMappable
      * The origin may be a number or a point, but the dispatched value will
      * always be a number; distance is computed using Pythagorean theorem.
      */
-    distanceFrom({ origin$ }: DistanceFromArgs<T>): ObservableWithMotionOperators<number> {
+    distanceFrom(origin$: DistanceFromOrigin<T>): ObservableWithMotionOperators<number>;
+    distanceFrom({ origin$ }: DistanceFromArgs<T>): ObservableWithMotionOperators<number>;
+    distanceFrom({ origin$ }: DistanceFromArgs<T> & DistanceFromOrigin<T>): ObservableWithMotionOperators<number> {
+      if (!isDefined(origin$)) {
+        origin$ = arguments[0] as DistanceFromOrigin<T>;
+      }
+
       return this._reactiveMap({
         transform({ upstream, origin }: Dict<(T & number) | (T & Point2D)>) {
           if (isPoint2D(upstream)) {