2015-12-09 07:57:17 +00:00
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2015-12-16 02:56:29 +00:00
< div class = "book" data-level = "6.6" data-chapter-title = "封裝" data-filepath = "ch6/ch6-06.md" data-basepath = ".." data-revision = "Wed Dec 16 2015 10:54:29 GMT+0800 (中国标准时间)" >
2015-12-09 07:57:17 +00:00
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前言
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< b > 0.1.< / b >
Go語言起源
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< b > 0.2.< / b >
Go語言項目
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< b > 0.3.< / b >
本書的組織
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< b > 0.4.< / b >
更多的信息
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< b > 0.5.< / b >
緻謝
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< b > 1.< / b >
入門
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< b > 1.1.< / b >
Hello, World
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< b > 1.2.< / b >
命令行參數
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< b > 1.3.< / b >
査找重復的行
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< b > 1.4.< / b >
GIF動畫
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< b > 1.5.< / b >
穫取URL
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< b > 1.6.< / b >
併髮穫取多個URL
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< b > 1.7.< / b >
Web服務
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< b > 1.8.< / b >
本章要點
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< b > 2.< / b >
程序結構
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< b > 2.1.< / b >
命名
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< li class = "chapter " data-level = "2.2" data-path = "ch2/ch2-02.html" >
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< b > 2.2.< / b >
聲明
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< b > 2.3.< / b >
變量
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< b > 2.4.< / b >
賦值
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< b > 2.5.< / b >
類型
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< b > 2.6.< / b >
包和文件
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< b > 2.7.< / b >
作用域
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< b > 3.< / b >
基礎數據類型
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< b > 3.1.< / b >
整型
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< b > 3.2.< / b >
浮點數
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< b > 3.3.< / b >
復數
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< b > 3.4.< / b >
佈爾型
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< b > 3.5.< / b >
字符串
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< b > 3.6.< / b >
常量
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< b > 4.< / b >
復閤數據類型
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< b > 4.1.< / b >
數組
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< b > 4.2.< / b >
切片
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< b > 4.3.< / b >
字典
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< b > 4.4.< / b >
結構體
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< b > 4.5.< / b >
JSON
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< b > 4.6.< / b >
文本和HTML模闆
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< li class = "chapter " data-level = "5" data-path = "ch5/ch5.html" >
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< b > 5.< / b >
函數
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< b > 5.1.< / b >
函數聲明
< / a >
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< li class = "chapter " data-level = "5.2" data-path = "ch5/ch5-02.html" >
< a href = "../ch5/ch5-02.html" >
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< b > 5.2.< / b >
遞歸
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< / li >
< li class = "chapter " data-level = "5.3" data-path = "ch5/ch5-03.html" >
< a href = "../ch5/ch5-03.html" >
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< b > 5.3.< / b >
多返迴值
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< li class = "chapter " data-level = "5.4" data-path = "ch5/ch5-04.html" >
< a href = "../ch5/ch5-04.html" >
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< b > 5.4.< / b >
錯誤
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< li class = "chapter " data-level = "5.5" data-path = "ch5/ch5-05.html" >
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< b > 5.5.< / b >
函數值
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< li class = "chapter " data-level = "5.6" data-path = "ch5/ch5-06.html" >
< a href = "../ch5/ch5-06.html" >
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< b > 5.6.< / b >
匿名函數
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< / li >
< li class = "chapter " data-level = "5.7" data-path = "ch5/ch5-07.html" >
< a href = "../ch5/ch5-07.html" >
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< b > 5.7.< / b >
可變參數
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< li class = "chapter " data-level = "5.8" data-path = "ch5/ch5-08.html" >
< a href = "../ch5/ch5-08.html" >
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< b > 5.8.< / b >
Deferred函數
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< li class = "chapter " data-level = "5.9" data-path = "ch5/ch5-09.html" >
< a href = "../ch5/ch5-09.html" >
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< b > 5.9.< / b >
Panic異常
< / a >
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< li class = "chapter " data-level = "5.10" data-path = "ch5/ch5-10.html" >
< a href = "../ch5/ch5-10.html" >
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< b > 5.10.< / b >
Recover捕穫異常
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< li class = "chapter " data-level = "6" data-path = "ch6/ch6.html" >
< a href = "../ch6/ch6.html" >
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< b > 6.< / b >
方法
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< li class = "chapter " data-level = "6.1" data-path = "ch6/ch6-01.html" >
< a href = "../ch6/ch6-01.html" >
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< b > 6.1.< / b >
方法聲明
< / a >
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< li class = "chapter " data-level = "6.2" data-path = "ch6/ch6-02.html" >
< a href = "../ch6/ch6-02.html" >
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< b > 6.2.< / b >
基於指鍼對象的方法
< / a >
< / li >
< li class = "chapter " data-level = "6.3" data-path = "ch6/ch6-03.html" >
< a href = "../ch6/ch6-03.html" >
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< b > 6.3.< / b >
通過嵌入結構體來擴展類型
< / a >
< / li >
< li class = "chapter " data-level = "6.4" data-path = "ch6/ch6-04.html" >
< a href = "../ch6/ch6-04.html" >
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< b > 6.4.< / b >
方法值和方法錶達式
< / a >
< / li >
< li class = "chapter " data-level = "6.5" data-path = "ch6/ch6-05.html" >
< a href = "../ch6/ch6-05.html" >
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< b > 6.5.< / b >
示例: Bit數組
< / a >
< / li >
< li class = "chapter active" data-level = "6.6" data-path = "ch6/ch6-06.html" >
< a href = "../ch6/ch6-06.html" >
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< b > 6.6.< / b >
封裝
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< / ul >
< / li >
< li class = "chapter " data-level = "7" data-path = "ch7/ch7.html" >
< a href = "../ch7/ch7.html" >
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< b > 7.< / b >
接口
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< ul class = "articles" >
< li class = "chapter " data-level = "7.1" data-path = "ch7/ch7-01.html" >
< a href = "../ch7/ch7-01.html" >
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< b > 7.1.< / b >
接口是閤約
< / a >
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< li class = "chapter " data-level = "7.2" data-path = "ch7/ch7-02.html" >
< a href = "../ch7/ch7-02.html" >
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< b > 7.2.< / b >
接口類型
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< li class = "chapter " data-level = "7.3" data-path = "ch7/ch7-03.html" >
< a href = "../ch7/ch7-03.html" >
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< b > 7.3.< / b >
實現接口的條件
< / a >
< / li >
< li class = "chapter " data-level = "7.4" data-path = "ch7/ch7-04.html" >
< a href = "../ch7/ch7-04.html" >
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< b > 7.4.< / b >
flag.Value接口
< / a >
< / li >
< li class = "chapter " data-level = "7.5" data-path = "ch7/ch7-05.html" >
< a href = "../ch7/ch7-05.html" >
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< b > 7.5.< / b >
接口值
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< li class = "chapter " data-level = "7.6" data-path = "ch7/ch7-06.html" >
< a href = "../ch7/ch7-06.html" >
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< b > 7.6.< / b >
sort.Interface接口
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< li class = "chapter " data-level = "7.7" data-path = "ch7/ch7-07.html" >
< a href = "../ch7/ch7-07.html" >
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< b > 7.7.< / b >
http.Handler接口
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< li class = "chapter " data-level = "7.8" data-path = "ch7/ch7-08.html" >
< a href = "../ch7/ch7-08.html" >
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< b > 7.8.< / b >
error接口
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< li class = "chapter " data-level = "7.9" data-path = "ch7/ch7-09.html" >
< a href = "../ch7/ch7-09.html" >
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< b > 7.9.< / b >
示例: 錶達式求值
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< li class = "chapter " data-level = "7.10" data-path = "ch7/ch7-10.html" >
< a href = "../ch7/ch7-10.html" >
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< b > 7.10.< / b >
類型斷言
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< li class = "chapter " data-level = "7.11" data-path = "ch7/ch7-11.html" >
< a href = "../ch7/ch7-11.html" >
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< b > 7.11.< / b >
基於類型斷言識彆錯誤類型
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< li class = "chapter " data-level = "7.12" data-path = "ch7/ch7-12.html" >
< a href = "../ch7/ch7-12.html" >
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< b > 7.12.< / b >
通過類型斷言査詢接口
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< li class = "chapter " data-level = "7.13" data-path = "ch7/ch7-13.html" >
< a href = "../ch7/ch7-13.html" >
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< b > 7.13.< / b >
類型分支
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< li class = "chapter " data-level = "7.14" data-path = "ch7/ch7-14.html" >
< a href = "../ch7/ch7-14.html" >
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< b > 7.14.< / b >
示例: 基於標記的XML解碼
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< li class = "chapter " data-level = "7.15" data-path = "ch7/ch7-15.html" >
< a href = "../ch7/ch7-15.html" >
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< b > 7.15.< / b >
補充幾點
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< li class = "chapter " data-level = "8" data-path = "ch8/ch8.html" >
< a href = "../ch8/ch8.html" >
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< b > 8.< / b >
Goroutines和Channels
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< li class = "chapter " data-level = "8.1" data-path = "ch8/ch8-01.html" >
< a href = "../ch8/ch8-01.html" >
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< b > 8.1.< / b >
Goroutines
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< li class = "chapter " data-level = "8.2" data-path = "ch8/ch8-02.html" >
< a href = "../ch8/ch8-02.html" >
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< b > 8.2.< / b >
示例: 併髮的Clock服務
< / a >
< / li >
< li class = "chapter " data-level = "8.3" data-path = "ch8/ch8-03.html" >
< a href = "../ch8/ch8-03.html" >
< i class = "fa fa-check" > < / i >
< b > 8.3.< / b >
示例: 併髮的Echo服務
< / a >
< / li >
< li class = "chapter " data-level = "8.4" data-path = "ch8/ch8-04.html" >
< a href = "../ch8/ch8-04.html" >
< i class = "fa fa-check" > < / i >
< b > 8.4.< / b >
Channels
< / a >
< / li >
< li class = "chapter " data-level = "8.5" data-path = "ch8/ch8-05.html" >
< a href = "../ch8/ch8-05.html" >
< i class = "fa fa-check" > < / i >
< b > 8.5.< / b >
併行的循環
< / a >
< / li >
< li class = "chapter " data-level = "8.6" data-path = "ch8/ch8-06.html" >
< a href = "../ch8/ch8-06.html" >
< i class = "fa fa-check" > < / i >
< b > 8.6.< / b >
示例: 併髮的Web爬蟲
< / a >
< / li >
< li class = "chapter " data-level = "8.7" data-path = "ch8/ch8-07.html" >
< a href = "../ch8/ch8-07.html" >
< i class = "fa fa-check" > < / i >
< b > 8.7.< / b >
基於select的多路復用
< / a >
< / li >
< li class = "chapter " data-level = "8.8" data-path = "ch8/ch8-08.html" >
< a href = "../ch8/ch8-08.html" >
< i class = "fa fa-check" > < / i >
< b > 8.8.< / b >
示例: 併髮的字典遍歷
< / a >
< / li >
< li class = "chapter " data-level = "8.9" data-path = "ch8/ch8-09.html" >
< a href = "../ch8/ch8-09.html" >
< i class = "fa fa-check" > < / i >
< b > 8.9.< / b >
併髮的退齣
< / a >
< / li >
< li class = "chapter " data-level = "8.10" data-path = "ch8/ch8-10.html" >
< a href = "../ch8/ch8-10.html" >
< i class = "fa fa-check" > < / i >
< b > 8.10.< / b >
示例: 聊天服務
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "9" data-path = "ch9/ch9.html" >
< a href = "../ch9/ch9.html" >
< i class = "fa fa-check" > < / i >
< b > 9.< / b >
基於共享變量的併髮
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "9.1" data-path = "ch9/ch9-01.html" >
< a href = "../ch9/ch9-01.html" >
< i class = "fa fa-check" > < / i >
< b > 9.1.< / b >
競爭條件
< / a >
< / li >
< li class = "chapter " data-level = "9.2" data-path = "ch9/ch9-02.html" >
< a href = "../ch9/ch9-02.html" >
< i class = "fa fa-check" > < / i >
< b > 9.2.< / b >
sync.Mutex互斥鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.3" data-path = "ch9/ch9-03.html" >
< a href = "../ch9/ch9-03.html" >
< i class = "fa fa-check" > < / i >
< b > 9.3.< / b >
sync.RWMutex讀寫鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.4" data-path = "ch9/ch9-04.html" >
< a href = "../ch9/ch9-04.html" >
< i class = "fa fa-check" > < / i >
< b > 9.4.< / b >
內存衕步
< / a >
< / li >
< li class = "chapter " data-level = "9.5" data-path = "ch9/ch9-05.html" >
< a href = "../ch9/ch9-05.html" >
< i class = "fa fa-check" > < / i >
< b > 9.5.< / b >
sync.Once初始化
< / a >
< / li >
< li class = "chapter " data-level = "9.6" data-path = "ch9/ch9-06.html" >
< a href = "../ch9/ch9-06.html" >
< i class = "fa fa-check" > < / i >
< b > 9.6.< / b >
競爭條件檢測
< / a >
< / li >
< li class = "chapter " data-level = "9.7" data-path = "ch9/ch9-07.html" >
< a href = "../ch9/ch9-07.html" >
< i class = "fa fa-check" > < / i >
< b > 9.7.< / b >
示例: 併髮的非阻塞緩存
< / a >
< / li >
< li class = "chapter " data-level = "9.8" data-path = "ch9/ch9-08.html" >
< a href = "../ch9/ch9-08.html" >
< i class = "fa fa-check" > < / i >
< b > 9.8.< / b >
Goroutines和綫程
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "10" data-path = "ch10/ch10.html" >
< a href = "../ch10/ch10.html" >
< i class = "fa fa-check" > < / i >
< b > 10.< / b >
包和工具
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "10.1" data-path = "ch10/ch10-01.html" >
< a href = "../ch10/ch10-01.html" >
< i class = "fa fa-check" > < / i >
< b > 10.1.< / b >
簡介
< / a >
< / li >
< li class = "chapter " data-level = "10.2" data-path = "ch10/ch10-02.html" >
< a href = "../ch10/ch10-02.html" >
< i class = "fa fa-check" > < / i >
< b > 10.2.< / b >
導入路徑
< / a >
< / li >
< li class = "chapter " data-level = "10.3" data-path = "ch10/ch10-03.html" >
< a href = "../ch10/ch10-03.html" >
< i class = "fa fa-check" > < / i >
< b > 10.3.< / b >
包聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.4" data-path = "ch10/ch10-04.html" >
< a href = "../ch10/ch10-04.html" >
< i class = "fa fa-check" > < / i >
< b > 10.4.< / b >
導入聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.5" data-path = "ch10/ch10-05.html" >
< a href = "../ch10/ch10-05.html" >
< i class = "fa fa-check" > < / i >
< b > 10.5.< / b >
匿名導入
< / a >
< / li >
< li class = "chapter " data-level = "10.6" data-path = "ch10/ch10-06.html" >
< a href = "../ch10/ch10-06.html" >
< i class = "fa fa-check" > < / i >
< b > 10.6.< / b >
包和命名
< / a >
< / li >
< li class = "chapter " data-level = "10.7" data-path = "ch10/ch10-07.html" >
< a href = "../ch10/ch10-07.html" >
< i class = "fa fa-check" > < / i >
< b > 10.7.< / b >
工具
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "11" data-path = "ch11/ch11.html" >
< a href = "../ch11/ch11.html" >
< i class = "fa fa-check" > < / i >
< b > 11.< / b >
測試
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "11.1" data-path = "ch11/ch11-01.html" >
< a href = "../ch11/ch11-01.html" >
< i class = "fa fa-check" > < / i >
< b > 11.1.< / b >
go test
< / a >
< / li >
< li class = "chapter " data-level = "11.2" data-path = "ch11/ch11-02.html" >
< a href = "../ch11/ch11-02.html" >
< i class = "fa fa-check" > < / i >
< b > 11.2.< / b >
測試函數
< / a >
< / li >
< li class = "chapter " data-level = "11.3" data-path = "ch11/ch11-03.html" >
< a href = "../ch11/ch11-03.html" >
< i class = "fa fa-check" > < / i >
< b > 11.3.< / b >
測試覆蓋率
< / a >
< / li >
< li class = "chapter " data-level = "11.4" data-path = "ch11/ch11-04.html" >
< a href = "../ch11/ch11-04.html" >
< i class = "fa fa-check" > < / i >
< b > 11.4.< / b >
基準測試
< / a >
< / li >
< li class = "chapter " data-level = "11.5" data-path = "ch11/ch11-05.html" >
< a href = "../ch11/ch11-05.html" >
< i class = "fa fa-check" > < / i >
< b > 11.5.< / b >
剖析
< / a >
< / li >
< li class = "chapter " data-level = "11.6" data-path = "ch11/ch11-06.html" >
< a href = "../ch11/ch11-06.html" >
< i class = "fa fa-check" > < / i >
< b > 11.6.< / b >
示例函數
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "12" data-path = "ch12/ch12.html" >
< a href = "../ch12/ch12.html" >
< i class = "fa fa-check" > < / i >
< b > 12.< / b >
反射
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "12.1" data-path = "ch12/ch12-01.html" >
< a href = "../ch12/ch12-01.html" >
< i class = "fa fa-check" > < / i >
< b > 12.1.< / b >
為何需要反射?
< / a >
< / li >
< li class = "chapter " data-level = "12.2" data-path = "ch12/ch12-02.html" >
< a href = "../ch12/ch12-02.html" >
< i class = "fa fa-check" > < / i >
< b > 12.2.< / b >
reflect.Type和reflect.Value
< / a >
< / li >
< li class = "chapter " data-level = "12.3" data-path = "ch12/ch12-03.html" >
< a href = "../ch12/ch12-03.html" >
< i class = "fa fa-check" > < / i >
< b > 12.3.< / b >
Display遞歸打印
< / a >
< / li >
< li class = "chapter " data-level = "12.4" data-path = "ch12/ch12-04.html" >
< a href = "../ch12/ch12-04.html" >
< i class = "fa fa-check" > < / i >
< b > 12.4.< / b >
示例: 編碼S錶達式
< / a >
< / li >
< li class = "chapter " data-level = "12.5" data-path = "ch12/ch12-05.html" >
< a href = "../ch12/ch12-05.html" >
< i class = "fa fa-check" > < / i >
< b > 12.5.< / b >
通過reflect.Value脩改值
< / a >
< / li >
< li class = "chapter " data-level = "12.6" data-path = "ch12/ch12-06.html" >
< a href = "../ch12/ch12-06.html" >
< i class = "fa fa-check" > < / i >
< b > 12.6.< / b >
示例: 解碼S錶達式
< / a >
< / li >
< li class = "chapter " data-level = "12.7" data-path = "ch12/ch12-07.html" >
< a href = "../ch12/ch12-07.html" >
< i class = "fa fa-check" > < / i >
< b > 12.7.< / b >
穫取結構體字段標識
< / a >
< / li >
< li class = "chapter " data-level = "12.8" data-path = "ch12/ch12-08.html" >
< a href = "../ch12/ch12-08.html" >
< i class = "fa fa-check" > < / i >
< b > 12.8.< / b >
顯示一個類型的方法集
< / a >
< / li >
< li class = "chapter " data-level = "12.9" data-path = "ch12/ch12-09.html" >
< a href = "../ch12/ch12-09.html" >
< i class = "fa fa-check" > < / i >
< b > 12.9.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "13" data-path = "ch13/ch13.html" >
< a href = "../ch13/ch13.html" >
< i class = "fa fa-check" > < / i >
< b > 13.< / b >
底層編程
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "13.1" data-path = "ch13/ch13-01.html" >
< a href = "../ch13/ch13-01.html" >
< i class = "fa fa-check" > < / i >
< b > 13.1.< / b >
unsafe.Sizeof, Alignof 和 Offsetof
< / a >
< / li >
< li class = "chapter " data-level = "13.2" data-path = "ch13/ch13-02.html" >
< a href = "../ch13/ch13-02.html" >
< i class = "fa fa-check" > < / i >
< b > 13.2.< / b >
unsafe.Pointer
< / a >
< / li >
< li class = "chapter " data-level = "13.3" data-path = "ch13/ch13-03.html" >
< a href = "../ch13/ch13-03.html" >
< i class = "fa fa-check" > < / i >
< b > 13.3.< / b >
示例: 深度相等判斷
< / a >
< / li >
< li class = "chapter " data-level = "13.4" data-path = "ch13/ch13-04.html" >
< a href = "../ch13/ch13-04.html" >
< i class = "fa fa-check" > < / i >
< b > 13.4.< / b >
通過cgo調用C代碼
< / a >
< / li >
< li class = "chapter " data-level = "13.5" data-path = "ch13/ch13-05.html" >
< a href = "../ch13/ch13-05.html" >
< i class = "fa fa-check" > < / i >
< b > 13.5.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "14" data-path = "exercise/ex.html" >
< a href = "../exercise/ex.html" >
< i class = "fa fa-check" > < / i >
< b > 14.< / b >
習題解答
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "14.1" data-path = "exercise/ex-ch1.html" >
< a href = "../exercise/ex-ch1.html" >
< i class = "fa fa-check" > < / i >
< b > 14.1.< / b >
第一章 入門
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "15" data-path = "errata.html" >
< a href = "../errata.html" >
< i class = "fa fa-check" > < / i >
< b > 15.< / b >
勘誤
< / a >
< / li >
< li class = "divider" > < / li >
< li >
< a href = "https://www.gitbook.com" target = "blank" class = "gitbook-link" >
本書使用 GitBook 釋出
< / a >
< / li >
< / ul >
< / nav >
< / div >
< div class = "book-body" >
< div class = "body-inner" >
< div class = "book-header" role = "navigation" >
<!-- Actions Left -->
<!-- Title -->
< h1 >
< i class = "fa fa-circle-o-notch fa-spin" > < / i >
< a href = "../" > Go编程语言< / a >
< / h1 >
< / div >
< div class = "page-wrapper" tabindex = "-1" role = "main" >
< div class = "page-inner" >
< section class = "normal" id = "section-" >
< h2 id = "66-封裝" > 6.6. 封 裝 < / h2 >
< p > 一 個 對 象 的 變 量 或 者 方 法 如 果 對 調 用 方 是 不 可 見 的 話 ， 一 般 就 被 定 義 為 “ 封 裝 ” 。 封 裝 有 時 候 也 被 叫 做 信 息 隱 藏 ， 衕 時 也 是 麫 曏 對 象 編 程 最 關 鍵 的 一 個 方 麫 。 < / p >
< p > Go語 言 隻 有 一 種 控 製 可 見 性 的 手 段 ： 大 寫 首 字 母 的 標 識 符 會 從 定 義 它 們 的 包 中 被 導 齣 ， 小 寫 字 母 的 則 不 會 。 這 種 限 製 包 內 成 員 的 方 式 衕 樣 適 用 於 struct或 者 一 個 類 型 的 方 法 。 因 而 如 果 我 們 想 要 封 裝 一 個 對 象 ， 我 們 必 鬚 將 其 定 義 為 一 個 struct。 < / p >
< p > 這 也 就 是 前 麫 的 小 節 中 IntSet被 定 義 為 struct類 型 的 原 因 ， 盡 管 它 隻 有 一 個 字 段 ： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > type< / span > IntSet < span class = "hljs-keyword" > struct< / span > {
words []< span class = "hljs-typename" > uint64< / span >
}
< / code > < / pre >
< p > 當 然 ， 我 們 也 可 以 把 IntSet定 義 為 一 個 slice類 型 ， 盡 管 這 樣 我 們 就 需 要 把 代 碼 中 所 有 方 法 裏 用 到 的 s.words用 *s替 換 掉 了 ： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > type< / span > IntSet []< span class = "hljs-typename" > uint64< / span >
< / code > < / pre >
< p > 盡 管 這 個 版 本 的 IntSet在 本 質 上 是 一 樣 的 ， 他 也 可 以 允 許 其 它 包 中 可 以 直 接 讀 取 併 編 輯 這 個 slice。 換 句 話 說 ， 相 對 *s這 個 錶 達 式 會 齣 現 在 所 有 的 包 中 ， s.words隻 需 要 在 定 義 IntSet的 包 中 齣 現 (譯 註 ： 所 以 還 是 推 薦 後 者 吧 的 意 思 )。 < / p >
< p > 這 種 基 於 名 字 的 手 段 使 得 在 語 言 中 最 小 的 封 裝 單 元 是 package， 而 不 是 像 其 它 語 言 一 樣 的 類 型 。 一 個 struct類 型 的 字 段 對 衕 一 個 包 的 所 有 代 碼 都 有 可 見 性 ， 無 論 你 的 代 碼 是 寫 在 一 個 函 數 還 是 一 個 方 法 裏 。 < / p >
< p > 封 裝 提 供 了 三 方 麫 的 優 點 。 首 先 ， 因 為 調 用 方 不 能 直 接 脩 改 對 象 的 變 量 值 ， 其 隻 需 要 關 註 少 量 的 語 句 併 且 隻 要 弄 懂 少 量 變 量 的 可 能 的 值 卽 可 。 < / p >
< p > 第 二 ， 隱 藏 實 現 的 細 節 ， 可 以 防 止 調 用 方 依 賴 那 些 可 能 變 化 的 具 體 實 現 ， 這 樣 使 設 計 包 的 程 序 員 在 不 破 壞 對 外 的 api情 況 下 能 得 到 更 大 的 自 由 。 < / p >
< p > 把 bytes.Buffer這 個 類 型 作 為 例 子 來 考 慮 。 這 個 類 型 在 做 短 字 符 串 疊 加 的 時 候 很 常 用 ， 所 以 在 設 計 的 時 候 可 以 做 一 些 預 先 的 優 化 ， 比 如 提 前 預 留 一 部 分 空 間 ， 來 避 免 反 復 的 內 存 分 配 。 又 因 為 Buffer是 一 個 struct類 型 ， 這 些 額 外 的 空 間 可 以 用 附 加 的 字 節 數 組 來 保 存 ， 且 放 在 一 個 小 寫 字 母 開 頭 的 字 段 中 。 這 樣 在 外 部 的 調 用 方 隻 能 看 到 性 能 的 提 陞 ， 但 併 不 會 得 到 這 個 附 加 變 量 。 Buffer和 其 增 長 算 法 我 們 列 在 這 裏 ， 為 了 簡 潔 性 稍 微 做 了 一 些 精 簡 ： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > type< / span > Buffer < span class = "hljs-keyword" > struct< / span > {
buf []< span class = "hljs-typename" > byte< / span >
initial [< span class = "hljs-number" > 64< / span > ]< span class = "hljs-typename" > byte< / span >
< span class = "hljs-comment" > /* ... */< / span >
}
< span class = "hljs-comment" > // Grow expands the buffer' s capacity, if necessary,< / span >
< span class = "hljs-comment" > // to guarantee space for another n bytes. [...]< / span >
< span class = "hljs-keyword" > func< / span > (b *Buffer) Grow(n < span class = "hljs-typename" > int< / span > ) {
< span class = "hljs-keyword" > if< / span > b.buf == < span class = "hljs-constant" > nil< / span > {
b.buf = b.initial[:< span class = "hljs-number" > 0< / span > ] < span class = "hljs-comment" > // use preallocated space initially< / span >
}
< span class = "hljs-keyword" > if< / span > < span class = "hljs-built_in" > len< / span > (b.buf)+n > < span class = "hljs-built_in" > cap< / span > (b.buf) {
buf := < span class = "hljs-built_in" > make< / span > ([]< span class = "hljs-typename" > byte< / span > , b.Len(), < span class = "hljs-number" > 2< / span > *< span class = "hljs-built_in" > cap< / span > (b.buf) + n)
< span class = "hljs-built_in" > copy< / span > (buf, b.buf)
b.buf = buf
}
}
< / code > < / pre >
< p > 封 裝 的 第 三 個 優 點 也 是 最 重 要 的 優 點 ， 是 阻 止 了 外 部 調 用 方 對 對 象 內 部 的 值 任 意 地 進 行 脩 改 。 因 為 對 象 內 部 變 量 隻 可 以 被 衕 一 個 包 內 的 函 數 脩 改 ， 所 以 包 的 作 者 可 以 讓 這 些 函 數 確 保 對 象 內 部 的 一 些 值 的 不 變 性 。 比 如 下 麫 的 Counter類 型 允 許 調 用 方 來 增 加 counter變 量 的 值 ， 併 且 允 許 將 這 個 值 reset為 0， 但 是 不 允 許 隨 便 設 置 這 個 值 (譯 註 ： 因 為 壓 根 就 訪 問 不 到 )： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > type< / span > Counter < span class = "hljs-keyword" > struct< / span > { n < span class = "hljs-typename" > int< / span > }
< span class = "hljs-keyword" > func< / span > (c *Counter) N() < span class = "hljs-typename" > int< / span > { < span class = "hljs-keyword" > return< / span > c.n }
< span class = "hljs-keyword" > func< / span > (c *Counter) Increment() { c.n++ }
< span class = "hljs-keyword" > func< / span > (c *Counter) Reset() { c.n = < span class = "hljs-number" > 0< / span > }
< / code > < / pre >
< p > 隻 用 來 訪 問 或 脩 改 內 部 變 量 的 函 數 被 稱 為 setter或 者 getter， 例 子 如 下 ， 比 如 log包 裏 的 Logger類 型 對 應 的 一 些 函 數 。 在 命 名 一 個 getter方 法 時 ， 我 們 通 常 會 省 略 掉 前 麫 的 Get前 綴 。 這 種 簡 潔 上 的 偏 好 也 可 以 推 廣 到 各 種 類 型 的 前 綴 比 如 Fetch， Find或 者 Lookup。 < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > package< / span > log
< span class = "hljs-keyword" > type< / span > Logger < span class = "hljs-keyword" > struct< / span > {
flags < span class = "hljs-typename" > int< / span >
prefix < span class = "hljs-typename" > string< / span >
< span class = "hljs-comment" > // ...< / span >
}
< span class = "hljs-keyword" > func< / span > (l *Logger) Flags() < span class = "hljs-typename" > int< / span >
< span class = "hljs-keyword" > func< / span > (l *Logger) SetFlags(flag < span class = "hljs-typename" > int< / span > )
< span class = "hljs-keyword" > func< / span > (l *Logger) Prefix() < span class = "hljs-typename" > string< / span >
< span class = "hljs-keyword" > func< / span > (l *Logger) SetPrefix(prefix < span class = "hljs-typename" > string< / span > )
< / code > < / pre >
< p > Go的 編 碼 風 格 不 禁 止 直 接 導 齣 字 段 。 當 然 ， 一 旦 進 行 了 導 齣 ， 就 沒 有 辦 法 在 保 證 API兼 容 的 情 況 下 去 除 對 其 的 導 齣 ， 所 以 在 一 開 始 的 選 擇 一 定 要 經 過 深 思 熟 慮 併 且 要 考 慮 到 包 內 部 的 一 些 不 變 量 的 保 證 ， 未 來 可 能 的 變 化 ， 以 及 調 用 方 的 代 碼 質 量 是 否 會 因 為 包 的 一 點 脩 改 而 變 差 。 < / p >
< p > 封 裝 併 不 總 是 理 想 的 。
雖 然 封 裝 在 有 些 情 況 是 必 要 的 ， 但 有 時 候 我 們 也 需 要 暴 露 一 些 內 部 內 容 ， 比 如 ： time.Duration將 其 錶 現 暴 露 為 一 個 int64數 字 的 納 秒 ， 使 得 我 們 可 以 用 一 般 的 數 值 操 作 來 對 時 間 進 行 對 比 ， 甚 至 可 以 定 義 這 種 類 型 的 常 量 ： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > const< / span > day = < span class = "hljs-number" > 24< / span > * time.Hour
fmt.Println(day.Seconds()) < span class = "hljs-comment" > // " 86400" < / span >
< / code > < / pre >
< p > 另 一 個 例 子 ， 將 IntSet和 本 章 開 頭 的 geometry.Path進 行 對 比 。 Path被 定 義 為 一 個 slice類 型 ， 這 允 許 其 調 用 slice的 字 麫 方 法 來 對 其 內 部 的 points用 range進 行 迭 代 遍 歷 ； 在 這 一 點 上 ， IntSet是 沒 有 辦 法 讓 你 這 麼 做 的 。 < / p >
< p > 這 兩 種 類 型 決 定 性 的 不 衕 ： geometry.Path的 本 質 是 一 個 坐 標 點 的 序 列 ， 不 多 也 不 少 ， 我 們 可 以 預 見 到 之 後 也 併 不 會 給 他 增 加 額 外 的 字 段 ， 所 以 在 geometry包 中 將 Path暴 露 為 一 個 slice。 相 比 之 下 ， IntSet僅 僅 是 在 這 裏 用 了 一 個 []uint64的 slice。 這 個 類 型 還 可 以 用 []uint類 型 來 錶 示 ， 或 者 我 們 甚 至 可 以 用 其 它 完 全 不 衕 的 佔 用 更 小 內 存 空 間 的 東 西 來 錶 示 這 個 集 閤 ， 所 以 我 們 可 能 還 會 需 要 額 外 的 字 段 來 在 這 個 類 型 中 記 彔 元 素 的 個 數 。 也 正 是 因 為 這 些 原 因 ， 我 們 讓 IntSet對 調 用 方 透 明 。 < / p >
< p > 在 這 章 中 ， 我 們 學 到 了 如 何 將 方 法 與 命 名 類 型 進 行 組 閤 ， 併 且 知 道 了 如 何 調 用 這 些 方 法 。 盡 管 方 法 對 於 OOP編 程 來 說 至 關 重 要 ， 但 他 們 隻 是 OOP編 程 裏 的 半 邊 天 。 為 了 完 成 OOP， 我 們 還 需 要 接 口 。 Go裏 的 接 口 會 在 下 一 章 中 介 紹 。 < / p >
< / section >
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< script src = "../gitbook/app.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-search/lunr.min.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-search/search.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-sharing/buttons.js" > < / script >
< script src = "../gitbook/plugins/gitbook-plugin-fontsettings/buttons.js" > < / script >
< script >
require(["gitbook"], function(gitbook) {
var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
gitbook.start(config);
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