slightly better types on the specs

Author: cormacrelf

packages/angular-skyhook/src/connection-types.ts

@@ -91,8 +91,8 @@ export interface ConnectionBase<TMonitor> extends SubscriptionLike {
  * To create one, refer to {@link SkyhookDndService#dropTarget}.
  */
 export interface DropTarget<
-  Item extends {} = {},
-  DropResult extends {} = {}
+  Item = {},
+  DropResult = {}
   > extends ConnectionBase<DropTargetMonitor<Item, DropResult>> {
 
   /** Use this method to have a dynamically typed target. If no type has
@@ -125,7 +125,7 @@ To create one, refer to {@link SkyhookDndService#dragSource}.
  */
 export interface DragSource<
   Item,
-  DropResult extends {} = {}
+  DropResult = {}
   > extends ConnectionBase<DragSourceMonitor<Item, DropResult>> {
 
   /** Use this method to have a dynamically typed source. If no type has

packages/angular-skyhook/src/connector.service.ts

@@ -131,8 +131,8 @@ export class SkyhookDndService {
    * {@link DropTarget#setTypes} in a lifecycle hook.
    */
   public dropTarget<
-    Item extends {} = {},
-    DropResult extends {} = {}
+    Item = {},
+    DropResult = {}
     >(
       types: TypeOrTypeArray | null,
       spec: DropTargetSpec<Item, DropResult>,
@@ -185,7 +185,7 @@ export class SkyhookDndService {
 
   public dragSource<
     Item,
-    DropResult extends {} = {}
+    DropResult = {}
     >(
       type: string | symbol | null,
       spec: DragSourceSpec<Item, DropResult>,

packages/angular-skyhook/src/drag-source-specification.ts

@@ -5,9 +5,16 @@
 
 import { DragSourceMonitor } from './source-monitor';
 
+/*
+Note that you can't infer Item if you supply both beginDrag and endDrag,
+since endDrag needs to find some type to put in the 'monitor' argument.
+But people can always nail it down with `dnd.dragSource<MyItemType>('BOX', { ...spec })`.
+Related: https://github.com/Microsoft/TypeScript/issues/19345
+*/
+
 export interface DragSourceSpec<
   Item,
-  DropResult extends {} = {}
+  DropResult = {}
   > {
 
   /**
@@ -21,13 +28,14 @@ export interface DragSourceSpec<
    * this.id }` from this method.
    *
    */
-  beginDrag(monitor: DragSourceMonitor<Item, DropResult>): Item;
+  // erase Item here because inference doesn't know what it is yet
+  beginDrag: (monitor: DragSourceMonitor<void, void>) => Item;
 
   /**
    * Optional. Queries your component to determine whether this source can be
    * dragged. Default returns true; this is often sufficient.
    */
-  canDrag?(monitor: DragSourceMonitor<Item, DropResult>): boolean;
+  canDrag?: (monitor: DragSourceMonitor<void, void>) => boolean;
 
   /** By default, only the drag source that initiated the drag operation is
    *  considered to be dragging. You might override this by matching on the
@@ -45,7 +53,7 @@ export interface DragSourceSpec<
    * immediately, and if you use `NgZone.run()` then you may experience
    * performance degradation..
    */
-  isDragging?(monitor: DragSourceMonitor<Item, DropResult>): boolean;
+  isDragging?: (monitor: DragSourceMonitor<Item, void>) => boolean;
 
   /**
    * Optional. Notifies your component when dragging ends.
@@ -54,5 +62,5 @@ export interface DragSourceSpec<
    * want to check {@link DragSourceMonitor#didDrop} and {@link DragSourceMonitor#getDropResult} for more
    * details.
    */
-  endDrag?(monitor: DragSourceMonitor<Item, DropResult>): void;
+  endDrag?: (monitor: DragSourceMonitor<Item, DropResult>) => void;
 }

packages/angular-skyhook/src/drop-target-specification.ts

@@ -19,13 +19,13 @@ export interface DropTargetSpec<
    *
    * Default, when not specified, is `true`.
    **/
-  canDrop?(monitor: DropTargetMonitor<Item, DropResult>): boolean;
+  canDrop?: (monitor: DropTargetMonitor<Item, DropResult>) => boolean;
 
   /** Called frequently while the mouse hovers over the owner drop target while
    * dragging a relevant item.
    *
    * */
-  hover?(monitor: DropTargetMonitor<Item, DropResult>): void;
+  hover?: (monitor: DropTargetMonitor<Item, DropResult>) => void;
 
   /** Called when a compatible item is dropped on the target. You may either
    *  return nothing, or a plain object.
@@ -44,6 +44,6 @@ export interface DropTargetSpec<
    * This method will not be called if `canDrop()` is defined and returns `false`.
    */
 
-  drop?(monitor: DropTargetMonitor<Item, DropResult>): DropResult | void;
+  drop?: (monitor: DropTargetMonitor<Item, DropResult>) => DropResult | void;
 
 }

packages/angular-skyhook/src/monitor-base.ts

@@ -8,7 +8,7 @@
 import { Offset } from './type-ish';
 import { Observable } from 'rxjs';
 
-export interface MonitorBase<Item extends {} = {}> {
+export interface MonitorBase<Item> {
 
   /** The type of the item in transit. Returns `null` if no item is being dragged. */
   getItemType(): string | symbol | null;

packages/angular-skyhook/src/source-monitor.ts

@@ -6,8 +6,8 @@
 import { MonitorBase } from './monitor-base';
 
 export interface DragSourceMonitor<
-  Item extends {} = {},
-  DropResult extends {} = {}
+  Item = {},
+  DropResult = {}
   > extends MonitorBase<Item> {
 
   /**
@@ -47,7 +47,7 @@ Instead, keep your `canDrag` logic simple, and replicate it in your template.
    * `drop()` overrides the child drop result previously set by the child.
    * Returns `null` if called outside `endDrag()`.
    */
-  getDropResult(): Object & any;
+  getDropResult(): DropResult;
 
   /**
    * Returns `true` if some drop target handled the `drop` event; `false`

packages/angular-skyhook/src/target-monitor.ts

@@ -6,8 +6,8 @@
 import { MonitorBase } from './monitor-base';
 
 export interface DropTargetMonitor<
-    Item extends {} = {},
-    DropResult extends {} = {}
+    Item = {},
+    DropResult = {}
     > extends MonitorBase<Item> {
     /**
      * Returns `true` if there is a drag operation in progress, and the owner's