From 5f86679158c13bd5636bb73d6cdb669d63ab85c1 Mon Sep 17 00:00:00 2001
From: Awin Huang <awinhuang@gmail.com>
Date: Tue, 21 Jun 2022 16:36:00 +0800
Subject: [PATCH] vault backup: 2022-06-21 16:36:00
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Affected files:
02. PARA/03. Resources（資源）/Design Pattern.md
---
 .../03. Resources（資源）/Design Pattern.md   | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/02. PARA/03. Resources（資源）/Design Pattern.md b/02. PARA/03. Resources（資源）/Design Pattern.md
index c822e15..3845fed 100644
--- a/02. PARA/03. Resources（資源）/Design Pattern.md	
+++ b/02. PARA/03. Resources（資源）/Design Pattern.md	
@@ -162,6 +162,11 @@ notify()則是當發生變化時，用來通知所有觀察者的實作。
     - 2
         ### Beverage class
         ```cpp
+        class Beverage {
+            int32_t cost() { return cost; }
+            int32_t cost;
+        }
+    
         class BeverageMilkTea { ... };
         class BeverageGreenTea { ... };
         class BeverageBlackTea {
@@ -184,13 +189,15 @@ class BeverageBlackTea {
 要算價格的時候：
 ```cpp
 class BeverageBlackTea {
-    void cost() {
-        if (bubble) cost += 10;
-        if (redbean) cost += 10;
-        if (greenbean) cost += 10;
-        if (fairyGrass) cost += 10;
+    int32_t cost() {
+        if (bubble) cost += 10;    // 珍珠要加10元
+        if (redbean) cost += 5;    // 紅豆要加10元
+        if (greenbean) cost += 7;  // 綠豆要加10元
+        if (fairyGrass) cost += 9; // 珍珠要加10元
+        return cost;
     }
-private:
     int32_t cost = 30;  // 奶茶本身10元
 };
-```
\ No newline at end of file
+```
+
+這樣的問題是，每當有一種新配料出現，我們就要在奶茶類別裡修改至少2個function，addXXX()與cost()，目前我們有3種飲料，所以要修改6個function，更何況，如果客人要加2份珍珠怎麼辦？這明顯不利程式的維護，必須有一種方法讓程式的修改最小，讓寫好的程式不用被修改才行。
\ No newline at end of file