feat(grid): pass cursor along with hexes in getPrevHexState() for a ~…

…20% performance increase

When traversing a grid more than once the cursor was determined by doing a complete iteration of the
previous traverser in order to get the last hex. The next traverser continues where the previous
traverser left off. Now, the cursor is also returned when the previous traverser is called. This
increases performance with ~20% when traversing a 10k hex grid twice.

src/grid/grid.ts

@@ -1,11 +1,11 @@
 import { createHex, Hex, HexCoordinates } from '../hex'
 import { NoopMap } from './noopMap'
 import { rectangle, RectangleOptions } from './traversers'
-import { eachCallbackFn, GetOrCreateHexFn, GetPrevHexesFn, GridStore, mapCallbackFn, Traverser } from './types'
+import { eachCallbackFn, GetOrCreateHexFn, GetPrevHexState, GridStore, mapCallbackFn, Traverser } from './types'
 
 export class Grid<T extends Hex> {
-  static of<T extends Hex>(hexPrototype: T, store?: GridStore<T>, getPrevHexes?: GetPrevHexesFn<T>) {
-    return new Grid<T>(hexPrototype, store, getPrevHexes)
+  static of<T extends Hex>(hexPrototype: T, store?: GridStore<T>, getPrevHexState?: GetPrevHexState<T>) {
+    return new Grid<T>(hexPrototype, store, getPrevHexState)
   }
 
   getOrCreateHex: GetOrCreateHexFn<T> = (coordinates) => {
@@ -16,48 +16,49 @@ export class Grid<T extends Hex> {
   constructor(
     public hexPrototype: T,
     public store: GridStore<T> = new NoopMap(),
-    private getPrevHexes: GetPrevHexesFn<T> = () => [],
+    private getPrevHexState: GetPrevHexState<T> = () => ({ hexes: [], cursor: null }),
   ) {}
 
   *[Symbol.iterator]() {
-    for (const hex of this.getPrevHexes()) {
+    for (const hex of this.getPrevHexState().hexes) {
       yield hex
     }
   }
 
   // it doesn't take a hexPrototype and store because it doesn't need to copy those
-  clone(getPrevHexes = this.getPrevHexes) {
-    // bind(this) in case the getPrevHexes is a "regular" (generator) function
-    return Grid.of(this.hexPrototype, this.store, getPrevHexes.bind(this))
+  clone(getPrevHexState = this.getPrevHexState) {
+    // bind(this) in case the getPrevHexState is a "regular" (generator) function
+    return Grid.of(this.hexPrototype, this.store, getPrevHexState.bind(this))
   }
 
   each(callback: eachCallbackFn<T>) {
     const each = () => {
-      const prevHexes = this.getPrevHexes()
-      for (const hex of prevHexes) {
+      const prevHexState = this.getPrevHexState()
+      for (const hex of prevHexState.hexes) {
         callback(hex, this)
       }
-      return prevHexes
+      return prevHexState
     }
 
     return this.clone(each)
   }
 
   map(callback: mapCallbackFn<T>) {
     const map = () => {
+      const { hexes, cursor } = this.getPrevHexState()
       const nextHexes: T[] = []
-      for (const hex of this.getPrevHexes()) {
+      for (const hex of hexes) {
         nextHexes.push(callback(hex, this))
       }
-      return nextHexes
+      return { hexes: nextHexes, cursor }
     }
 
     return this.clone(map)
   }
 
   // todo: alias to take or takeUntil?
   run(stopFn: (hex: T) => boolean = () => false) {
-    for (const hex of this.getPrevHexes()) {
+    for (const hex of this.getPrevHexState().hexes) {
       if (stopFn(hex)) {
         return this
       }
@@ -78,9 +79,9 @@ export class Grid<T extends Hex> {
       return this
     }
 
-    const traverse: GetPrevHexesFn<T> = () => {
+    const traverse: GetPrevHexState<T> = () => {
       const nextHexes: T[] = []
-      let cursor = Array.from(this.getPrevHexes()).pop() ?? createHex(this.hexPrototype).clone() // clone to enable users to make custom hexes
+      let cursor = this.getPrevHexState().cursor ?? createHex(this.hexPrototype).clone() // clone to enable users to make custom hexes
 
       for (const traverser of traversers) {
         for (const nextCursor of traverser(cursor, this.getOrCreateHex)) {
@@ -89,7 +90,7 @@ export class Grid<T extends Hex> {
         }
       }
 
-      return nextHexes
+      return { hexes: nextHexes, cursor }
     }
 
     return this.clone(traverse)

src/grid/types.ts

@@ -1,8 +1,13 @@
 import { Hex, HexCoordinates } from '../hex'
 import { Grid } from './grid'
 
-export interface GetPrevHexesFn<T extends Hex> {
-  (this: Grid<T>): Iterable<T>
+export interface PrevHexState<T extends Hex> {
+  hexes: Iterable<T>
+  cursor: T | null
+}
+
+export interface GetPrevHexState<T extends Hex> {
+  (this: Grid<T>): PrevHexState<T>
 }
 
 export interface Traverser<T extends Hex> {