From e1de21036af7b422fe117eb0df17f540fc6ebb26 Mon Sep 17 00:00:00 2001
From: Kuitos <kuitos.lau@gmail.com>
Date: Sat, 14 Apr 2018 00:25:58 +0800
Subject: [PATCH 1/2] avoid the unnecessary reassign with the equivalent
 comparison result

---
 src/core/computedvalue.ts | 12 +++++++++---
 test/base/babel-tests.js  | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/src/core/computedvalue.ts b/src/core/computedvalue.ts
index 8e9826d7a..7da1fafa7 100644
--- a/src/core/computedvalue.ts
+++ b/src/core/computedvalue.ts
@@ -197,13 +197,19 @@ export class ComputedValue<T> implements IObservable, IComputedValue<T>, IDeriva
         const oldValue = this.value
         const wasSuspended =
             /* see #1208 */ this.dependenciesState === IDerivationState.NOT_TRACKING
-        const newValue = (this.value = this.computeValue(true))
-        return (
+        const newValue = this.computeValue(true)
+
+        const changed =
             wasSuspended ||
             isCaughtException(oldValue) ||
             isCaughtException(newValue) ||
             !this.equals(oldValue, newValue)
-        )
+
+        if (changed) {
+            this.value = newValue
+        }
+
+        return changed
     }
 
     computeValue(track: boolean) {
diff --git a/test/base/babel-tests.js b/test/base/babel-tests.js
index 4d78789b4..8d066a117 100644
--- a/test/base/babel-tests.js
+++ b/test/base/babel-tests.js
@@ -102,6 +102,29 @@ test("babel: parameterized computed decorator", () => {
     expect(changes).toEqual([{ sum: 6 }, { sum: 7 }, { sum: 9 }])
 })
 
+test("computed value should be the same around comparer judged equivalent reassign", () => {
+    class TestClass {
+        @observable c = null
+        defaultCollection = []
+        @computed.struct
+        get collection() {
+            return this.c || this.defaultCollection
+        }
+    }
+
+    const t1 = new TestClass()
+
+    const d = autorun(() => t1.collection)
+
+    const oldCollection = t1.collection
+    t1.c = []
+    const newCollection = t1.collection
+
+    expect(oldCollection).toBe(newCollection)
+
+    d()
+})
+
 class Order {
     @observable price = 3
     @observable amount = 2

From cff477c8bbc2757e5e53d77aa621f5cccf09b193 Mon Sep 17 00:00:00 2001
From: Kuitos <kuitos.lau@gmail.com>
Date: Sat, 14 Apr 2018 01:17:07 +0800
Subject: [PATCH 2/2] reword the test case description

---
 test/base/babel-tests.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/base/babel-tests.js b/test/base/babel-tests.js
index 8d066a117..d5f20c4f6 100644
--- a/test/base/babel-tests.js
+++ b/test/base/babel-tests.js
@@ -102,7 +102,7 @@ test("babel: parameterized computed decorator", () => {
     expect(changes).toEqual([{ sum: 6 }, { sum: 7 }, { sum: 9 }])
 })
 
-test("computed value should be the same around comparer judged equivalent reassign", () => {
+test("computed value should be the same around changing which was considered equivalent", () => {
     class TestClass {
         @observable c = null
         defaultCollection = []