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< title > 示例: 編碼S表達式 | Go语言圣经< / title >
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前言
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Go語言起源
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Go語言項目
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本書的組織
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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" >
< li class = "chapter " data-level = "4.1" data-path = "ch4/ch4-01.html" >
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< b > 4.1.< / b >
數組
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< b > 4.2.< / b >
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Slice
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< li class = "chapter " data-level = "4.3" data-path = "ch4/ch4-03.html" >
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< b > 4.3.< / b >
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Map
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< li class = "chapter " data-level = "4.4" data-path = "ch4/ch4-04.html" >
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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" >
< a href = "../ch5/ch5.html" >
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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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< 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 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 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" >
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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" >
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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" >
< a href = "../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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< li class = "chapter " data-level = "6.1" data-path = "ch6/ch6-01.html" >
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< b > 6.1.< / b >
方法聲明
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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 >
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基於指針對象的方法
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< / a >
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< 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 >
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< 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 >
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方法值和方法表達式
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< / a >
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< 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
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< li class = "chapter " 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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< 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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< li class = "chapter " data-level = "7.2" data-path = "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" >
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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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< 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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< 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 >
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示例: 表達式求值
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< / a >
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< li class = "chapter " data-level = "7.10" data-path = "ch7/ch7-10.html" >
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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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< / a >
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< li class = "chapter " data-level = "7.12" data-path = "ch7/ch7-12.html" >
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< b > 7.12.< / b >
通過類型斷言査詢接口
< / a >
< / li >
< li class = "chapter " data-level = "7.13" data-path = "ch7/ch7-13.html" >
< a href = "../ch7/ch7-13.html" >
< i class = "fa fa-check" > < / i >
< b > 7.13.< / b >
類型分支
< / a >
< / 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 active" 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 >
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< a href = "../" > Go语言圣经< / a >
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< / h1 >
< / div >
< div class = "page-wrapper" tabindex = "-1" role = "main" >
< div class = "page-inner" >
< section class = "normal" id = "section-" >
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< h2 id = "124-示例-編碼s表達式" > 12.4. 示 例 : 編 碼 S表 達 式 < / h2 >
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< p > Display是 一 個 用 於 顯 示 結 構 化 數 據 的 調 試 工 具 ， 但 是 它 併 不 能 將 任 意 的 Go語 言 對 象 編 碼 爲 通 用 消 息 然 後 用 於 進 程 間 通 信 。 < / p >
< p > 正 如 我 們 在 4.5節 中 中 看 到 的 ， Go語 言 的 標 準 庫 支 持 了 包 括 JSON、 XML和 ASN.1等 多 種 編 碼 格 式 。 還 有 另 一 種 依 然 被 廣 泛 使 用 的 格 式 是 S表 達 式 格 式 ， 采 用 類 似 Lisp語 言 的 語 法 。 但 是 和 其 他 編 碼 格 式 不 同 的 是 ， Go語 言 自 帶 的 標 準 庫 併 不 支 持 S表 達 式 ， 主 要 是 因 爲 它 沒 有 一 個 公 認 的 標 準 規 范 。 < / p >
< p > 在 本 節 中 ， 我 們 將 定 義 一 個 包 用 於 將 Go語 言 的 對 象 編 碼 爲 S表 達 式 格 式 ， 它 支 持 以 下 結 構 ： < / p >
< pre > < code > 42 integer
" hello" string (with Go-style quotation)
foo symbol (an unquoted name)
(1 2 3) list (zero or more items enclosed in parentheses)
< / code > < / pre > < p > 布 爾 型 習 慣 上 使 用 t符 號 表 示 true， 空 列 表 或 nil符 號 表 示 false， 但 是 爲 了 簡 單 起 見 ， 我 們 暫 時 忽 略 布 爾 類 型 。 同 時 忽 略 的 還 有 chan管 道 和 函 數 ， 因 爲 通 過 反 射 併 無 法 知 道 它 們 的 確 切 狀 態 。 我 們 忽 略 的 還 浮 點 數 、 複 數 和 interface。 支 持 它 們 是 練 習 12.3的 任 務 。 < / p >
< p > 我 們 將 Go語 言 的 類 型 編 碼 爲 S表 達 式 的 方 法 如 下 。 整 數 和 字 符 串 以 自 然 的 方 式 編 碼 。 Nil值 編 碼 爲 nil符 號 。 數 組 和 slice被 編 碼 爲 一 個 列 表 。 < / p >
< p > 結 構 體 被 編 碼 爲 成 員 對 象 的 列 表 ， 每 個 成 員 對 象 對 應 一 個 個 僅 有 兩 個 元 素 的 子 列 表 ， 其 中 子 列 表 的 第 一 個 元 素 是 成 員 的 名 字 ， 子 列 表 的 第 二 個 元 素 是 成 員 的 值 。 Map被 編 碼 爲 鍵 值 對 的 列 表 。 傳 統 上 ， S表 達 式 使 用 點 狀 符 號 列 表 (key . value)結 構 來 表 示 key/value對 ， 而 不 是 用 一 個 含 雙 元 素 的 列 表 ， 不 過 爲 了 簡 單 我 們 忽 略 了 點 狀 符 號 列 表 。 < / p >
< p > 編 碼 是 由 一 個 encode遞 歸 函 數 完 成 ， 如 下 所 示 。 它 的 結 構 本 質 上 和 前 面 的 Display函 數 類 似 ： < / p >
< pre > < code class = "lang-Go" > gopl.io/ch12/sexpr
< span class = "hljs-keyword" > func< / span > encode(buf *bytes.Buffer, v reflect.Value) error {
< span class = "hljs-keyword" > switch< / span > v.Kind() {
< span class = "hljs-keyword" > case< / span > reflect.Invalid:
buf.WriteString(< span class = "hljs-string" > " nil" < / span > )
< span class = "hljs-keyword" > case< / span > reflect.Int, reflect.Int8, reflect.Int16,
reflect.Int32, reflect.Int64:
fmt.Fprintf(buf, < span class = "hljs-string" > " %d" < / span > , v.Int())
< span class = "hljs-keyword" > case< / span > reflect.Uint, reflect.Uint8, reflect.Uint16,
reflect.Uint32, reflect.Uint64, reflect.Uintptr:
fmt.Fprintf(buf, < span class = "hljs-string" > " %d" < / span > , v.Uint())
< span class = "hljs-keyword" > case< / span > reflect.String:
fmt.Fprintf(buf, < span class = "hljs-string" > " %q" < / span > , v.String())
< span class = "hljs-keyword" > case< / span > reflect.Ptr:
< span class = "hljs-keyword" > return< / span > encode(buf, v.Elem())
< span class = "hljs-keyword" > case< / span > reflect.Array, reflect.Slice: < span class = "hljs-comment" > // (value ...)< / span >
buf.WriteByte(< span class = "hljs-string" > ' (' < / span > )
< span class = "hljs-keyword" > for< / span > i := < span class = "hljs-number" > 0< / span > ; i < v.Len(); i++ {
< span class = "hljs-keyword" > if< / span > i > < span class = "hljs-number" > 0< / span > {
buf.WriteByte(< span class = "hljs-string" > ' ' < / span > )
}
< span class = "hljs-keyword" > if< / span > err := encode(buf, v.Index(i)); err != < span class = "hljs-constant" > nil< / span > {
< span class = "hljs-keyword" > return< / span > err
}
}
buf.WriteByte(< span class = "hljs-string" > ' )' < / span > )
< span class = "hljs-keyword" > case< / span > reflect.Struct: < span class = "hljs-comment" > // ((name value) ...)< / span >
buf.WriteByte(< span class = "hljs-string" > ' (' < / span > )
< span class = "hljs-keyword" > for< / span > i := < span class = "hljs-number" > 0< / span > ; i < v.NumField(); i++ {
< span class = "hljs-keyword" > if< / span > i > < span class = "hljs-number" > 0< / span > {
buf.WriteByte(< span class = "hljs-string" > ' ' < / span > )
}
fmt.Fprintf(buf, < span class = "hljs-string" > " (%s " < / span > , v.Type().Field(i).Name)
< span class = "hljs-keyword" > if< / span > err := encode(buf, v.Field(i)); err != < span class = "hljs-constant" > nil< / span > {
< span class = "hljs-keyword" > return< / span > err
}
buf.WriteByte(< span class = "hljs-string" > ' )' < / span > )
}
buf.WriteByte(< span class = "hljs-string" > ' )' < / span > )
< span class = "hljs-keyword" > case< / span > reflect.Map: < span class = "hljs-comment" > // ((key value) ...)< / span >
buf.WriteByte(< span class = "hljs-string" > ' (' < / span > )
< span class = "hljs-keyword" > for< / span > i, key := < span class = "hljs-keyword" > range< / span > v.MapKeys() {
< span class = "hljs-keyword" > if< / span > i > < span class = "hljs-number" > 0< / span > {
buf.WriteByte(< span class = "hljs-string" > ' ' < / span > )
}
buf.WriteByte(< span class = "hljs-string" > ' (' < / span > )
< span class = "hljs-keyword" > if< / span > err := encode(buf, key); err != < span class = "hljs-constant" > nil< / span > {
< span class = "hljs-keyword" > return< / span > err
}
buf.WriteByte(< span class = "hljs-string" > ' ' < / span > )
< span class = "hljs-keyword" > if< / span > err := encode(buf, v.MapIndex(key)); err != < span class = "hljs-constant" > nil< / span > {
< span class = "hljs-keyword" > return< / span > err
}
buf.WriteByte(< span class = "hljs-string" > ' )' < / span > )
}
buf.WriteByte(< span class = "hljs-string" > ' )' < / span > )
< span class = "hljs-keyword" > default< / span > : < span class = "hljs-comment" > // float, complex, bool, chan, func, interface< / span >
< span class = "hljs-keyword" > return< / span > fmt.Errorf(< span class = "hljs-string" > " unsupported type: %s" < / span > , v.Type())
}
< span class = "hljs-keyword" > return< / span > < span class = "hljs-constant" > nil< / span >
}
< / code > < / pre >
< p > Marshal函 數 是 對 encode的 保 證 ， 以 保 持 和 encoding/...下 其 它 包 有 着 相 似 的 API： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-comment" > // Marshal encodes a Go value in S-expression form.< / span >
< span class = "hljs-keyword" > func< / span > Marshal(v < span class = "hljs-keyword" > interface< / span > {}) ([]< span class = "hljs-typename" > byte< / span > , error) {
< span class = "hljs-keyword" > var< / span > buf bytes.Buffer
< span class = "hljs-keyword" > if< / span > err := encode(& buf, reflect.ValueOf(v)); err != < span class = "hljs-constant" > nil< / span > {
< span class = "hljs-keyword" > return< / span > < span class = "hljs-constant" > nil< / span > , err
}
< span class = "hljs-keyword" > return< / span > buf.Bytes(), < span class = "hljs-constant" > nil< / span >
}
< / code > < / pre >
< p > 下 面 是 Marshal對 12.3節 的 strangelove變 量 編 碼 後 的 結 果 ： < / p >
< pre > < code > ((Title " Dr. Strangelove" ) (Subtitle " How I Learned to Stop Worrying and Lo
ve the Bomb" ) (Year 1964) (Actor ((" Grp. Capt. Lionel Mandrake" " Peter Sell
ers" ) (" Pres. Merkin Muffley" " Peter Sellers" ) (" Gen. Buck Turgidson" " Geor
ge C. Scott" ) (" Brig. Gen. Jack D. Ripper" " Sterling Hayden" ) (" Maj. T.J. \
" King\" Kong" " Slim Pickens" ) (" Dr. Strangelove" " Peter Sellers" ))) (Oscars
(" Best Actor (Nomin.)" " Best Adapted Screenplay (Nomin.)" " Best Director (N
omin.)" " Best Picture (Nomin.)" )) (Sequel nil))
< / code > < / pre > < p > 整 個 輸 出 編 碼 爲 一 行 中 以 減 少 輸 出 的 大 小 ， 但 是 也 很 難 閲 讀 。 這 里 有 一 個 對 S表 達 式 格 式 化 的 約 定 。 編 寫 一 個 S表 達 式 的 格 式 化 函 數 將 作 爲 一 個 具 有 挑 戰 性 的 練 習 任 務 ； 不 過 < a href = "http://gopl.io" target = "_blank" > http://gopl.io< / a > 也 提 供 了 一 個 簡 單 的 版 本 。 < / p >
< pre > < code > ((Title " Dr. Strangelove" )
(Subtitle " How I Learned to Stop Worrying and Love the Bomb" )
(Year 1964)
(Actor ((" Grp. Capt. Lionel Mandrake" " Peter Sellers" )
(" Pres. Merkin Muffley" " Peter Sellers" )
(" Gen. Buck Turgidson" " George C. Scott" )
(" Brig. Gen. Jack D. Ripper" " Sterling Hayden" )
(" Maj. T.J. \" King\" Kong" " Slim Pickens" )
(" Dr. Strangelove" " Peter Sellers" )))
(Oscars (" Best Actor (Nomin.)"
" Best Adapted Screenplay (Nomin.)"
" Best Director (Nomin.)"
" Best Picture (Nomin.)" ))
(Sequel nil))
< / code > < / pre > < p > 和 fmt.Print、 json.Marshal、 Display函 數 類 似 ， sexpr.Marshal函 數 處 理 帶 環 的 數 據 結 構 也 會 陷 入 死 循 環 。 < / p >
< p > 在 12.6節 中 ， 我 們 將 給 出 S表 達 式 解 碼 器 的 實 現 步 驟 ， 但 是 在 那 之 前 ， 我 們 還 需 要 先 了 解 如 果 通 過 反 射 技 術 來 更 新 程 序 的 變 量 。 < / p >
< p > < strong > 練 習 12.3： < / strong > 實 現 encode函 數 缺 少 的 分 支 。 將 布 爾 類 型 編 碼 爲 t和 nil， 浮 點 數 編 碼 爲 Go語 言 的 格 式 ， 複 數 1+2i編 碼 爲 #C(1.0 2.0)格 式 。 接 口 編 碼 爲 類 型 名 和 值 對 ， 例 如 (" []int" (1 2 3))， 但 是 這 個 形 式 可 能 會 造 成 歧 義 ： reflect.Type.String方 法 對 於 不 同 的 類 型 可 能 返 迴 相 同 的 結 果 。 < / p >
< p > < strong > 練 習 12.4： < / strong > 脩 改 encode函 數 ， 以 上 面 的 格 式 化 形 式 輸 出 S表 達 式 。 < / p >
< p > < strong > 練 習 12.5： < / strong > 脩 改 encode函 數 ， 用 JSON格 式 代 替 S表 達 式 格 式 。 然 後 使 用 標 準 庫 提 供 的 json.Unmarshal解 碼 器 來 驗 證 函 數 是 正 確 的 。 < / p >
< p > < strong > 練 習 12.6： < / strong > 脩 改 encode， 作 爲 一 個 優 化 ， 忽 略 對 是 零 值 對 象 的 編 碼 。 < / p >
< p > < strong > 練 習 12.7： < / strong > 創 建 一 個 基 於 流 式 的 API， 用 於 S表 達 式 的 解 碼 ， 和 json.Decoder(§ 4.5)函 數 功 能 類 似 。 < / p >
2015-12-09 07:57:17 +00:00
< / section >
< / div >
< / div >
< / div >
< a href = "../ch12/ch12-03.html" class = "navigation navigation-prev " aria-label = "Previous page: Display遞歸打印" > < i class = "fa fa-angle-left" > < / i > < / a >
< a href = "../ch12/ch12-05.html" class = "navigation navigation-next " aria-label = "Next page: 通過reflect.Value脩改值" > < 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 >
