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< div class = "book" data-level = "2.4" data-chapter-title = "賦值" data-filepath = "ch2/ch2-04.md" data-basepath = ".." data-revision = "Thu Dec 24 2015 14:42:02 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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< / li >
< li class = "chapter " data-level = "1.4" data-path = "ch1/ch1-04.html" >
< a href = "../ch1/ch1-04.html" >
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< b > 1.4.< / b >
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GIF動畵
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< b > 1.5.< / b >
穫取URL
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< b > 1.6.< / b >
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併發穫取多個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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< 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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< / a >
< 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 >
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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< li class = "chapter " data-level = "4.6" data-path = "ch4/ch4-06.html" >
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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
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< li class = "chapter " data-level = "5.2" data-path = "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" >
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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" >
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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" >
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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" >
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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 >
Recover捕穫異常
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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" >
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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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< 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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< 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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< li class = "chapter " data-level = "6.6" data-path = "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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< li class = "chapter " data-level = "7.4" data-path = "ch7/ch7-04.html" >
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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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< 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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< 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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< b > 7.14.< / b >
示例: 基於標記的XML解碼
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< / 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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併發的退齣
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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 >
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 >
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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 = "24-賦值" > 2.4. 賦 值 < / h2 >
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< p > 使 用 賦 值 語 句 可 以 更 新 一 個 變 量 的 值 , 最 簡 單 的 賦 值 語 句 是 將 要 被 賦 值 的 變 量 放 在 < code > =< / code > 的 左 邊 , 新 值 的 表 達 式 放 在 < code > =< / code > 右 邊 .< / p >
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< pre > < code class = "lang-Go" > x = < span class = "hljs-number" > 1< / span > < span class = "hljs-comment" > // 命 令 變 量 的 賦 值 < / span >
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*p = < span class = "hljs-constant" > true< / span > < span class = "hljs-comment" > // 通 過 指 針 間 接 賦 值 < / span >
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person.name = < span class = "hljs-string" > " bob" < / span > < span class = "hljs-comment" > // 結 構 體 字 段 賦 值 < / span >
count[x] = count[x] * scale < span class = "hljs-comment" > // 數 組 , 切 片 或 字 典 的 元 素 賦 值 < / span >
< / code > < / pre >
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< p > 特 定 的 賦 值 語 句 和 二 元 算 術 複 合 操 作 有 一 個 簡 潔 形 式 , 例 如 上 面 最 後 的 語 句 可 以 重 寫 爲 :< / p >
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< pre > < code class = "lang-Go" > count[x] *= scale
< / code > < / pre >
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< p > 這 樣 可 以 省 去 對 變 量 表 達 式 的 重 複 計 算 .< / p >
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< p > 數 值 變 量 也 可 以 支 持 < code > ++< / code > 遞 增 和 < code > --< / code > 遞 減 語 句 :< / p >
< pre > < code class = "lang-Go" > v := < span class = "hljs-number" > 1< / span >
v++ < span class = "hljs-comment" > // 等 價 方 式 v = v + 1; v 變 成 2 < / span >
v-- < span class = "hljs-comment" > // 等 價 方 式 v = v - 1; v 變 成 1< / span >
< / code > < / pre >
< h3 id = "241-元組賦值" > 2.4.1. 元 組 賦 值 < / h3 >
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< p > 元 組 賦 值 是 另 一 種 形 式 的 賦 值 語 句 , 允 許 同 時 更 新 多 個 變 量 的 值 . 在 賦 值 之 前 , 賦 值 語 句 右 邊 的 所 有 表 達 式 將 會 先 進 行 求 值 , 然 後 再 統 一 更 新 左 邊 變 量 的 值 . 這 對 於 處 理 有 些 同 時 齣 現 在 元 組 賦 值 語 句 左 右 兩 邊 的 變 量 很 有 幫 助 , 例 如 我 們 可 以 這 樣 交 換 兩 個 變 量 的 值 :< / p >
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< pre > < code class = "lang-Go" > x, y = y, x
a[i], a[j] = a[j], a[i]
< / code > < / pre >
< p > 或 者 是 計 算 兩 個 整 數 值 的 的 最 大 公 約 數 (GCD):< / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > func< / span > gcd(x, y < span class = "hljs-typename" > int< / span > ) < span class = "hljs-typename" > int< / span > {
< span class = "hljs-keyword" > for< / span > y != < span class = "hljs-number" > 0< / span > {
x, y = y, x%y
}
< span class = "hljs-keyword" > return< / span > x
}
< / code > < / pre >
< p > 或 者 是 計 算 斐 波 納 契 數 列 (Fibonacci)的 第 N個 數 :< / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > func< / span > fib(n < span class = "hljs-typename" > int< / span > ) < span class = "hljs-typename" > int< / span > {
x, y := < span class = "hljs-number" > 0< / span > , < span class = "hljs-number" > 1< / span >
< span class = "hljs-keyword" > for< / span > i := < span class = "hljs-number" > 0< / span > ; i < n; i++ {
x, y = y, x+y
}
< span class = "hljs-keyword" > return< / span > x
}
< / code > < / pre >
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< p > 元 組 賦 值 也 可 以 使 一 繫 列 瑣 碎 賦 值 更 緊 湊 (譯 註 : 特 别 是 在 for循 環 的 初 始 化 部 分 ),< / p >
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< pre > < code class = "lang-Go" > i, j, k = < span class = "hljs-number" > 2< / span > , < span class = "hljs-number" > 3< / span > , < span class = "hljs-number" > 5< / span >
< / code > < / pre >
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< p > 但 如 果 表 達 式 太 複 雜 的 話 , 應 該 盡 量 避 免 元 組 賦 值 ; 因 爲 一 個 個 單 獨 的 賦 值 語 句 的 可 讀 性 會 更 好 .< / p >
< p > 某 些 表 達 式 會 産 生 多 個 值 , 比 如 調 用 一 個 有 多 個 返 迴 值 的 函 數 .
當 這 樣 一 個 函 數 調 用 齣 現 在 元 組 賦 值 右 邊 的 表 達 式 中 時 (譯 註 : 右 邊 不 能 再 有 其 他 表 達 式 ), 左 邊 變 量 的 數 目 必 鬚 和 右 邊 一 致 .< / p >
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< pre > < code class = "lang-Go" > f, err = os.Open(< span class = "hljs-string" > " foo.txt" < / span > ) < span class = "hljs-comment" > // function call returns two values< / span >
< / code > < / pre >
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< p > 通 常 , 這 類 函 數 會 用 額 外 的 返 迴 值 表 達 某 種 錯 誤 類 型 , 例 如 os.Open 是 返 迴 一 個 error 類 型 的 錯 誤 , 還 有 一 些 是 返 迴 布 爾 值 , 通 常 被 稱 爲 ok. 在 稍 後 我 們 看 到 的 三 個 操 作 都 是 類 似 的 行 爲 . 如 果 字 典 査 找 (§ 4.3), 類 型 斷 言 (§ 7.10), 或 通 道 接 收 (§ 8.4.2) 齣 現 在 賦 值 語 句 的 右 邊 , 它 們 都 將 産 生 兩 個 結 果 , 有 一 個 額 外 的 布 爾 結 果 表 示 操 作 是 否 成 功 :< / p >
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< pre > < code class = "lang-Go" > v, ok = m[key] < span class = "hljs-comment" > // map lookup< / span >
v, ok = x.(T) < span class = "hljs-comment" > // type assertion< / span >
v, ok = < -ch < span class = "hljs-comment" > // channel receive< / span >
< / code > < / pre >
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< p > 和 變 量 的 聲 明 一 樣 , 我 們 可 以 用 下 劃 線 空 白 標 識 符 < code > _< / code > 來 丟 棄 不 需 要 的 值 .< / p >
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< pre > < code class = "lang-Go" > _, err = io.Copy(dst, src) < span class = "hljs-comment" > // 丟 棄 字 節 數 < / span >
_, ok = x.(T) < span class = "hljs-comment" > // 隻 檢 測 類 型 , 忽 略 具 體 值 < / span >
< / code > < / pre >
< h3 id = "242-可賦值性" > 2.4.2. 可 賦 值 性 < / h3 >
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< p > 賦 值 語 句 是 顯 示 的 賦 值 形 式 , 但 是 程 序 中 還 有 很 多 地 方 會 發 送 隱 式 的 賦 值 行 爲 : 函 數 調 用 將 隱 式 地 將 調 用 參 數 的 值 賦 值 給 函 數 的 參 數 變 量 , 一 個 返 迴 語 句 將 隱 式 地 將 返 迴 操 作 的 值 賦 值 給 結 果 變 量 , 一 個 複 合 類 型 的 字 面 量 (§ 4.2)也 會 産 生 賦 值 行 爲 . 例 如 下 面 的 語 句 :< / p >
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< pre > < code class = "lang-Go" > medals := []< span class = "hljs-typename" > string< / span > {< span class = "hljs-string" > " gold" < / span > , < span class = "hljs-string" > " silver" < / span > , < span class = "hljs-string" > " bronze" < / span > }
< / code > < / pre >
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< p > 隱 式 地 對 切 片 的 每 個 元 素 進 行 賦 值 操 作 , 類 似 這 樣 寫 的 行 爲 :< / p >
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< pre > < code class = "lang-Go" > medals[< span class = "hljs-number" > 0< / span > ] = < span class = "hljs-string" > " gold" < / span >
medals[< span class = "hljs-number" > 1< / span > ] = < span class = "hljs-string" > " silver" < / span >
medals[< span class = "hljs-number" > 2< / span > ] = < span class = "hljs-string" > " bronze" < / span >
< / code > < / pre >
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< p > 字 典 和 管 道 的 元 素 , 雖 然 不 是 普 通 的 變 量 , 但 是 也 有 類 似 的 隱 式 賦 值 行 爲 .< / p >
< p > 不 管 是 隱 式 還 是 顯 示 地 賦 值 , 在 賦 值 語 句 坐 標 的 變 量 和 右 邊 最 終 的 求 到 的 值 必 鬚 有 相 同 的 數 據 類 型 . 更 直 白 地 説 , 隻 有 右 邊 的 值 對 於 左 邊 的 變 量 是 可 賦 值 的 , 賦 值 語 句 纔 是 允 許 的 .< / p >
< p > 可 賦 值 性 的 規 則 對 於 不 同 類 型 有 不 同 要 求 , 對 每 個 新 類 型 有 關 的 地 方 我 們 會 專 門 解 釋 .
對 於 目 前 我 們 已 經 討 論 過 的 類 型 , 它 的 規 則 是 簡 單 的 : 類 型 必 鬚 完 全 匹 配 , nil 可 以 賦 值 給 任 何 指 針 或 引 用 類 型 的 變 量 . 常 量 (§ 3.6)有 更 靈 活 的 規 則 , 這 樣 可 以 避 免 不 必 要 的 顯 示 類 型 轉 換 .< / p >
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< p > 對 於 兩 個 值 是 否 可 以 用 < code > ==< / code > 或 < code > !=< / code > 進 行 相 等 比 較 的 能 力 也 和 可 賦 值 能 力 有 關 繫 :
對 於 任 何 的 比 較 , 第 一 個 操 作 必 鬚 是 可 用 於 第 二 個 操 作 類 型 的 變 量 的 賦 值 的 , 反 之 依 然 .
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和 前 面 一 樣 , 我 們 會 對 每 個 新 類 型 比 較 有 關 的 地 方 會 做 專 門 解 釋 .< / p >
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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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< / script >
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