From e1a7e0329cbc51f5eb4d05a034760f936ea9ffe1 Mon Sep 17 00:00:00 2001
From: Brian Ford <btford@umich.edu>
Date: Sun, 30 Aug 2015 21:20:18 -0700
Subject: [PATCH] feat(router): hash-cons ComponentInstructions

---
 modules/angular2/src/router/instruction.ts    |  6 ++++
 .../angular2/src/router/path_recognizer.ts    | 31 ++++++++++++++-----
 .../test/router/path_recognizer_spec.ts       | 11 +++++++
 3 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/modules/angular2/src/router/instruction.ts b/modules/angular2/src/router/instruction.ts
index a2a6525c5b..f669d23332 100644
--- a/modules/angular2/src/router/instruction.ts
+++ b/modules/angular2/src/router/instruction.ts
@@ -83,6 +83,12 @@ function stringifyAux(instruction: Instruction): string {
  *
  * `ComponentInstructions` is a public API. Instances of `ComponentInstruction` are passed
  * to route lifecycle hooks, like {@link CanActivate}.
+ *
+ * `ComponentInstruction`s are [https://en.wikipedia.org/wiki/Hash_consing](hash consed). You should
+ * never construct one yourself with "new." Instead, rely on {@link PathRecognizer} to construct
+ * `ComponentInstruction`s.
+ *
+ * You should not modify this object. It should be treated as immutable.
  */
 export class ComponentInstruction {
   reuse: boolean = false;
diff --git a/modules/angular2/src/router/path_recognizer.ts b/modules/angular2/src/router/path_recognizer.ts
index 63592d9526..7b7757d2f9 100644
--- a/modules/angular2/src/router/path_recognizer.ts
+++ b/modules/angular2/src/router/path_recognizer.ts
@@ -192,6 +192,8 @@ export class PathRecognizer {
   specificity: number;
   terminal: boolean = true;
   hash: string;
+  private cache: Map<string, ComponentInstruction> = new Map<string, ComponentInstruction>();
+
 
   // TODO: cache component instruction instances by params and by ParsedUrl instance
 
@@ -252,23 +254,26 @@ export class PathRecognizer {
 
     var auxiliary;
     var instruction: ComponentInstruction;
+    var urlParams;
+    var allParams;
     if (isPresent(currentSegment)) {
       // If this is the root component, read query params. Otherwise, read matrix params.
       var paramsSegment = beginningSegment instanceof RootUrl ? beginningSegment : currentSegment;
 
-      var allParams = isPresent(paramsSegment.params) ?
-                          StringMapWrapper.merge(paramsSegment.params, positionalParams) :
-                          positionalParams;
+      allParams = isPresent(paramsSegment.params) ?
+                      StringMapWrapper.merge(paramsSegment.params, positionalParams) :
+                      positionalParams;
 
-      var urlParams = serializeParams(paramsSegment.params);
+      urlParams = serializeParams(paramsSegment.params);
 
-      instruction = new ComponentInstruction(urlPath, urlParams, this, allParams);
 
       auxiliary = currentSegment.auxiliary;
     } else {
-      instruction = new ComponentInstruction(urlPath, [], this, positionalParams);
+      allParams = positionalParams;
       auxiliary = [];
+      urlParams = [];
     }
+    instruction = this._getInstruction(urlPath, urlParams, this, allParams);
     return new PathMatch(instruction, nextSegment, auxiliary);
   }
 
@@ -289,6 +294,18 @@ export class PathRecognizer {
     var nonPositionalParams = paramTokens.getUnused();
     var urlParams = serializeParams(nonPositionalParams);
 
-    return new ComponentInstruction(urlPath, urlParams, this, params);
+    return this._getInstruction(urlPath, urlParams, this, params);
+  }
+
+  private _getInstruction(urlPath: string, urlParams: List<string>, _recognizer: PathRecognizer,
+                          params: StringMap<string, any>): ComponentInstruction {
+    var hashKey = urlPath + '?' + urlParams.join('?');
+    if (this.cache.has(hashKey)) {
+      return this.cache.get(hashKey);
+    }
+    var instruction = new ComponentInstruction(urlPath, urlParams, _recognizer, params);
+    this.cache.set(hashKey, instruction);
+
+    return instruction;
   }
 }
diff --git a/modules/angular2/test/router/path_recognizer_spec.ts b/modules/angular2/test/router/path_recognizer_spec.ts
index 5a577dd686..dbe1ecb4fb 100644
--- a/modules/angular2/test/router/path_recognizer_spec.ts
+++ b/modules/angular2/test/router/path_recognizer_spec.ts
@@ -40,6 +40,17 @@ export function main() {
           .toThrowError(`Path "hi//there" contains "//" which is not allowed in a route config.`);
     });
 
+    it('should return the same instruction instance when recognizing the same path', () => {
+      var rec = new PathRecognizer('/one', mockRouteHandler);
+
+      var one = new Url('one', null, null, {});
+
+      var firstMatch = rec.recognize(one);
+      var secondMatch = rec.recognize(one);
+
+      expect(firstMatch.instruction).toBe(secondMatch.instruction);
+    });
+
     describe('querystring params', () => {
       it('should parse querystring params so long as the recognizer is a root', () => {
         var rec = new PathRecognizer('/hello/there', mockRouteHandler);