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< div class = "book" data-level = "4.1" data-chapter-title = "數組" data-filepath = "ch4/ch4-01.md" data-basepath = ".." data-revision = "Mon Dec 28 2015 16:03:52 GMT+0800 (中国标准时间)" >
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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 >
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致謝
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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 >
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査找重複的行
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< b > 1.4.< / b >
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GIF動畵
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< b > 1.5.< / b >
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獲取URL
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< b > 1.6.< / b >
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併發獲取多個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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< 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 >
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複數
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< b > 3.4.< / b >
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布爾型
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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 >
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複合數據類型
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< ul class = "articles" >
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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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< b > 5.< / b >
函數
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< b > 5.1.< / b >
函數聲明
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< b > 5.2.< / b >
遞歸
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< b > 5.3.< / b >
多返迴值
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< b > 5.4.< / b >
錯誤
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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" >
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< b > 5.6.< / b >
匿名函數
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< b > 5.7.< / b >
可變參數
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< b > 5.8.< / b >
Deferred函數
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< b > 5.9.< / b >
Panic異常
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< li class = "chapter " data-level = "5.10" data-path = "ch5/ch5-10.html" >
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< b > 5.10.< / b >
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Recover捕獲異常
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< b > 6.< / b >
方法
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< b > 6.1.< / b >
方法聲明
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< b > 6.2.< / b >
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基於指針對象的方法
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< li class = "chapter " data-level = "6.3" data-path = "ch6/ch6-03.html" >
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< b > 6.3.< / b >
通過嵌入結構體來擴展類型
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< a href = "../ch6/ch6-04.html" >
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< b > 6.4.< / b >
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方法值和方法表達式
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< li class = "chapter " data-level = "6.5" data-path = "ch6/ch6-05.html" >
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< b > 6.5.< / b >
示例: Bit數組
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< b > 6.6.< / b >
封裝
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< b > 7.< / b >
接口
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< b > 7.1.< / b >
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接口是合約
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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" >
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< b > 7.3.< / b >
實現接口的條件
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< b > 7.4.< / b >
flag.Value接口
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< b > 7.5.< / b >
接口值
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< b > 7.6.< / b >
sort.Interface接口
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< b > 7.7.< / b >
http.Handler接口
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< b > 7.8.< / b >
error接口
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< b > 7.9.< / b >
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示例: 表達式求值
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< b > 7.10.< / b >
類型斷言
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< b > 7.11.< / b >
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基於類型斷言識别錯誤類型
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< b > 7.12.< / b >
通過類型斷言査詢接口
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< b > 7.13.< / b >
類型分支
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< / li >
< li class = "chapter " data-level = "7.14" data-path = "ch7/ch7-14.html" >
< a href = "../ch7/ch7-14.html" >
< i class = "fa fa-check" > < / i >
< b > 7.14.< / b >
示例: 基於標記的XML解碼
< / a >
< / li >
< li class = "chapter " data-level = "7.15" data-path = "ch7/ch7-15.html" >
< a href = "../ch7/ch7-15.html" >
< i class = "fa fa-check" > < / i >
< b > 7.15.< / b >
補充幾點
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "8" data-path = "ch8/ch8.html" >
< a href = "../ch8/ch8.html" >
< i class = "fa fa-check" > < / i >
< b > 8.< / b >
Goroutines和Channels
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "8.1" data-path = "ch8/ch8-01.html" >
< a href = "../ch8/ch8-01.html" >
< i class = "fa fa-check" > < / i >
< b > 8.1.< / b >
Goroutines
< / a >
< / li >
< li class = "chapter " data-level = "8.2" data-path = "ch8/ch8-02.html" >
< a href = "../ch8/ch8-02.html" >
< i class = "fa fa-check" > < / i >
< b > 8.2.< / b >
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示例: 併發的Clock服務
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< / 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 >
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示例: 併發的Echo服務
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< / 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 >
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示例: 併發的Web爬蟲
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< / 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 >
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基於select的多路複用
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< / 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 >
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示例: 併發的字典遍歷
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< / 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 >
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併發的退出
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< / 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 >
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基於共享變量的併發
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< / 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 >
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內存同步
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< / 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 >
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示例: 併發的非阻塞緩存
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< / 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 >
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Goroutines和線程
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< / 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 >
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爲何需要反射?
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< / 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 >
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示例: 編碼S表達式
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< / 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 >
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示例: 解碼S表達式
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< / 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 >
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獲取結構體字段標識
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< / 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 >
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< li class = "chapter " data-level = "14" data-path = "CONTRIBUTORS.html" >
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2015-12-24 06:47:06 +00:00
< a href = "../CONTRIBUTORS.html" >
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< i class = "fa fa-check" > < / i >
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< b > 14.< / b >
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附録
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< / 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 = "41-數組" > 4.1. 數 組 < / h2 >
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< p > 數 組 是 一 個 固 定 長 度 的 特 定 類 型 元 素 組 成 的 序 列 ， 有 零 個 或 多 個 元 素 。 因 爲 數 組 的 長 度 是 固 定 的 ， 因 此 在 Go語 言 中 很 少 直 接 使 用 數 組 。 Slice（ 切 片 ） ， 是 可 以 增 長 和 收 縮 動 態 序 列 ， slice功 能 也 更 靈 活 ， 但 是 要 理 解 slice工 作 原 理 的 話 需 要 先 理 解 數 組 。 < / p >
< p > 數 組 的 每 個 元 素 可 以 通 過 下 標 來 訪 問 ， 下 標 的 范 圍 是 從 0開 始 到 數 組 長 度 減 1的 位 置 。 內 置 的 len函 數 將 返 迴 數 組 中 元 素 的 個 數 。 < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > var< / span > a [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > < span class = "hljs-comment" > // array of 3 integers< / span >
fmt.Println(a[< span class = "hljs-number" > 0< / span > ]) < span class = "hljs-comment" > // print the first element< / span >
fmt.Println(a[< span class = "hljs-built_in" > len< / span > (a)-< span class = "hljs-number" > 1< / span > ]) < span class = "hljs-comment" > // print the last element, a[2]< / span >
< span class = "hljs-comment" > // Print the indices and elements.< / span >
< span class = "hljs-keyword" > for< / span > i, v := < span class = "hljs-keyword" > range< / span > a {
fmt.Printf(< span class = "hljs-string" > " %d %d\n" < / span > , i, v)
}
< span class = "hljs-comment" > // Print the elements only.< / span >
< span class = "hljs-keyword" > for< / span > _, v := < span class = "hljs-keyword" > range< / span > a {
fmt.Printf(< span class = "hljs-string" > " %d\n" < / span > , v)
}
< / code > < / pre >
< p > 默 認 情 況 下 ， 數 組 的 每 個 元 素 都 被 初 始 化 爲 元 素 類 型 對 應 的 零 值 ， 對 於 數 字 類 型 來 説 就 是 0。 我 們 可 以 使 用 數 組 字 面 值 語 法 用 一 組 值 來 初 始 化 數 組 ： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > var< / span > q [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > = [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > , < span class = "hljs-number" > 3< / span > }
< span class = "hljs-keyword" > var< / span > r [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > = [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > }
fmt.Println(r[< span class = "hljs-number" > 2< / span > ]) < span class = "hljs-comment" > // " 0" < / span >
< / code > < / pre >
< p > 在 數 組 字 面 值 中 ， 如 果 數 組 的 長 度 位 置 出 現 的 是 “ ...” 省 略 號 ， 則 表 示 數 組 的 長 度 是 根 據 初 始 化 值 的 個 數 來 計 算 的 。 上 面 q數 組 的 定 義 可 以 簡 化 爲 < / p >
< pre > < code class = "lang-Go" > q := [...]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > , < span class = "hljs-number" > 3< / span > }
fmt.Printf(< span class = "hljs-string" > " %T\n" < / span > , q) < span class = "hljs-comment" > // " [3]int" < / span >
< / code > < / pre >
< p > 數 組 的 長 度 是 數 組 類 型 的 一 個 組 成 部 分 ， 因 此 [3]int和 [4]int是 兩 種 不 同 的 數 組 類 型 。 數 組 的 長 度 必 鬚 是 常 量 表 達 式 ， 因 爲 數 組 的 長 度 需 要 在 程 序 的 編 譯 階 段 確 定 。 < / p >
< pre > < code class = "lang-Go" > q := [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > , < span class = "hljs-number" > 3< / span > }
q = [< span class = "hljs-number" > 4< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > , < span class = "hljs-number" > 3< / span > , < span class = "hljs-number" > 4< / span > } < span class = "hljs-comment" > // compile error: cannot assign [4]int to [3]int< / span >
< / code > < / pre >
< p > 我 們 將 會 發 現 ， 數 組 、 slice、 map和 結 構 體 字 面 值 的 寫 法 都 很 相 似 。 上 面 的 形 式 是 直 接 提 順 序 供 初 始 化 值 序 列 ， 但 是 也 可 以 指 定 一 個 索 引 和 對 應 值 的 列 表 初 始 化 ， 像 下 面 這 樣 ： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > type< / span > Currency < span class = "hljs-typename" > int< / span >
< span class = "hljs-keyword" > const< / span > (
USD Currency = < span class = "hljs-constant" > iota< / span > < span class = "hljs-comment" > // 美 元 < / span >
EUR < span class = "hljs-comment" > // 歐 元 < / span >
GBP < span class = "hljs-comment" > // 英 鎊 < / span >
RMB < span class = "hljs-comment" > // 人 民 幣 < / span >
)
symbol := [...]< span class = "hljs-typename" > string< / span > {USD: < span class = "hljs-string" > " $" < / span > , EUR: < span class = "hljs-string" > " € " < / span > , GBP: < span class = "hljs-string" > " ￡ " < / span > , RMB: < span class = "hljs-string" > " ￥ " < / span > }
fmt.Println(RMB, symbol[RMB]) < span class = "hljs-comment" > // " 3 " " < / span >
< / code > < / pre >
< p > 這 種 形 式 的 數 組 字 面 值 形 式 中 ， 初 始 化 索 引 的 順 序 是 無 關 緊 要 的 ， 而 且 一 些 索 引 可 以 省 略 ， 和 前 面 提 到 的 規 則 一 樣 ， 未 知 道 初 始 值 的 元 素 將 用 零 值 初 始 化 。 例 如 ， < / p >
< pre > < code class = "lang-Go" > r := [...]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 99< / span > : -< span class = "hljs-number" > 1< / span > }
< / code > < / pre >
< p > 定 義 了 一 個 含 有 100個 原 始 的 數 組 r， 最 後 一 個 元 素 初 始 化 爲 -1， 其 它 元 素 都 是 用 0初 始 化 。 < / p >
< p > 如 果 一 個 數 組 的 元 素 類 型 是 可 以 相 互 比 較 的 ， 那 麽 數 組 類 型 也 是 可 以 相 互 比 較 的 ， 因 此 我 們 可 以 直 接 通 過 ==比 較 運 算 符 來 比 較 兩 個 數 組 ， 隻 有 當 兩 個 數 組 的 所 有 元 素 都 是 相 等 的 時 候 數 組 才 是 相 等 的 。 相 對 的 是 不 相 等 比 較 運 算 符 !=。 < / p >
< pre > < code class = "lang-Go" > a := [< span class = "hljs-number" > 2< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > }
b := [...]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > }
c := [< span class = "hljs-number" > 2< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 3< / span > }
fmt.Println(a == b, a == c, b == c) < span class = "hljs-comment" > // " true false false" < / span >
d := [< span class = "hljs-number" > 3< / span > ]< span class = "hljs-typename" > int< / span > {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > }
fmt.Println(a == d) < span class = "hljs-comment" > // compile error: cannot compare [2]int == [3]int< / span >
< / code > < / pre >
< p > 作 爲 一 個 更 可 信 的 例 子 ， crypto/sha256包 的 Sum256函 數 用 於 生 成 一 個 針 對 任 意 的 字 節 類 型 的 slice消 息 的 摘 要 。 消 息 摘 要 有 256bit大 小 ， 因 此 對 應 [32]byte數 組 類 型 。 如 果 兩 個 消 息 摘 要 是 相 同 的 ， 那 麽 可 以 認 爲 兩 個 消 息 本 身 也 是 相 同 （ 譯 註 ： 理 論 上 有 HASH碼 碰 撞 的 清 空 ， 但 是 實 際 應 用 可 以 基 本 忽 略 ） ； 如 果 消 息 摘 要 不 同 ， 那 麽 消 息 本 身 比 如 也 是 不 同 的 。 下 面 的 例 子 用 SHA256算 法 分 别 生 成 “ x” 和 “ X” 兩 個 信 息 的 摘 要 ： < / p >
< pre > < code class = "lang-Go" > gopl.io/ch4/sha256
< span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " crypto/sha256" < / span >
< span class = "hljs-keyword" > func< / span > main() {
c1 := sha256.Sum256([]< span class = "hljs-typename" > byte< / span > (< span class = "hljs-string" > " x" < / span > ))
c2 := sha256.Sum256([]< span class = "hljs-typename" > byte< / span > (< span class = "hljs-string" > " X" < / span > ))
fmt.Printf(< span class = "hljs-string" > " %x\n%x\n%t\n%T\n" < / span > , c1, c2, c1 == c2, c1)
< span class = "hljs-comment" > // Output:< / span >
< span class = "hljs-comment" > // 2d711642b726b04401627ca9fbac32f5c8530fb1903cc4db02258717921a4881< / span >
< span class = "hljs-comment" > // 4b68ab3847feda7d6c62c1fbcbeebfa35eab7351ed5e78f4ddadea5df64b8015< / span >
< span class = "hljs-comment" > // false< / span >
< span class = "hljs-comment" > // [32]uint8< / span >
}
< / code > < / pre >
< p > 兩 個 消 息 雖 然 隻 有 一 個 字 符 的 差 異 ， 但 是 生 成 的 消 息 摘 要 則 幾 乎 有 一 半 的 bit位 是 不 同 的 。 需 要 註 意 Printf函 數 的 %x參 數 ， 它 用 於 指 定 以 十 六 進 製 的 格 式 打 印 全 部 的 數 組 或 slice的 的 元 素 ， %t參 數 是 用 於 打 印 布 爾 型 數 據 ， %T參 數 是 用 於 顯 示 一 個 值 對 應 的 數 據 類 型 。 < / p >
< p > 當 調 用 一 個 函 數 的 時 候 ， 函 數 的 每 個 調 用 參 數 將 會 被 賦 值 給 函 數 本 身 的 參 數 變 量 ， 所 以 函 數 參 數 變 量 接 收 的 是 一 個 複 製 的 副 本 ， 併 不 是 原 始 調 用 的 參 數 。 因 爲 函 數 參 數 傳 遞 的 機 製 導 致 傳 遞 大 的 數 組 類 型 將 是 低 效 的 ， 併 且 對 數 組 參 數 的 任 何 的 脩 改 都 是 發 生 在 複 製 的 數 組 上 ， 併 不 是 直 接 脩 改 調 用 時 原 始 的 數 組 變 量 。 在 這 個 方 面 ， Go語 言 對 待 數 組 的 方 式 和 其 它 很 多 編 程 語 言 不 同 ， 其 它 編 程 語 言 可 能 會 隱 式 地 將 數 組 作 爲 引 用 或 指 針 對 象 傳 入 被 調 用 的 函 數 。 < / p >
< p > 當 然 ， 我 們 可 以 顯 式 地 傳 入 一 個 數 組 指 針 ， 那 樣 的 話 函 數 對 數 組 的 任 何 脩 改 都 可 以 直 接 反 饋 到 調 用 者 。 下 面 的 函 數 用 於 給 [32]byte類 型 的 數 組 清 零 ： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > func< / span > zero(ptr *[< span class = "hljs-number" > 32< / span > ]< span class = "hljs-typename" > byte< / span > ) {
< span class = "hljs-keyword" > for< / span > i := < span class = "hljs-keyword" > range< / span > ptr {
ptr[i] = < span class = "hljs-number" > 0< / span >
}
}
< / code > < / pre >
< p > 其 實 數 組 字 面 值 [32]byte{}就 可 以 生 成 一 個 32字 節 的 數 組 。 而 且 每 個 數 組 的 元 素 都 是 零 值 初 始 化 ， 也 就 是 0。 我 們 可 以 將 上 面 的 zero函 數 寫 的 更 簡 潔 一 點 ： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > func< / span > zero(ptr *[< span class = "hljs-number" > 32< / span > ]< span class = "hljs-typename" > byte< / span > ) {
*ptr = [< span class = "hljs-number" > 32< / span > ]< span class = "hljs-typename" > byte< / span > {}
}
< / code > < / pre >
< p > 雖 然 通 過 指 針 來 傳 遞 數 組 參 數 是 高 效 的 ， 而 且 也 允 許 在 函 數 內 部 脩 改 數 組 的 值 ， 但 是 因 爲 數 組 依 然 是 殭 化 的 類 型 ， 因 爲 數 組 的 類 型 包 含 長 度 信 息 。 zero函 數 併 不 能 接 收 指 向 [16]byte類 型 數 組 的 指 針 ， 而 且 也 沒 有 任 何 添 加 或 刪 除 數 組 元 素 的 方 法 。 由 於 這 些 原 因 ， 除 了 像 SHA256這 類 需 要 處 理 特 定 大 小 數 組 的 函 數 外 ， 數 組 依 然 很 少 用 作 函 數 參 數 ； 相 反 ， 我 們 一 般 使 用 slice來 替 代 數 組 。 < / p >
< p > < strong > 練 習 4.1： < / strong > 編 寫 一 個 函 數 ， 計 算 兩 個 SHA256碼 中 不 同 bit的 數 目 。 （ 參 考 2.6.2節 的 PopCount函 數 。 )< / p >
< p > < strong > 練 習 4.2： < / strong > 編 寫 一 個 程 序 ， 默 認 打 印 標 準 輸 入 的 以 SHA256哈 希 碼 ， 也 可 以 通 過 命 令 行 標 準 參 數 選 擇 SHA384或 SHA512哈 希 算 法 。 < / p >
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< / section >
< / div >
< / div >
< / div >
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< a href = "../ch4/ch4.html" class = "navigation navigation-prev " aria-label = "Previous page: 複合數據類型" > < i class = "fa fa-angle-left" > < / i > < / a >
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< a href = "../ch4/ch4-02.html" class = "navigation navigation-next " aria-label = "Next page: 切片" > < i class = "fa fa-angle-right" > < / i > < / a >
< / div >
< / div >
< script src = "../gitbook/app.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) {
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var config = {"katex":{},"highlight":{},"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}};
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gitbook.start(config);
});
< / script >
< / body >
< / html >
