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< div class = "book" data-level = "2.5" data-chapter-title = "類型" data-filepath = "ch2/ch2-05.md" data-basepath = ".." data-revision = "Thu Dec 31 2015 16:18:40 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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< 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" >
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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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< 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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< b > 5.5.< / b >
函數值
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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 >
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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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< 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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< 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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< 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 " 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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< 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 = "25-類型" > 2.5. 類 型 < / h2 >
< p > 變 量 或 表 達 式 的 類 型 定 義 了 對 應 存 儲 值 的 屬 性 特 徵 ， 例 如 數 值 在 內 存 的 存 儲 大 小 （ 或 者 是 元 素 的 bit個 數 ） ， 它 們 在 內 部 是 如 何 表 達 的 ， 是 否 支 持 一 些 操 作 符 ， 以 及 它 們 自 己 關 聯 的 方 法 集 等 。 < / p >
< p > 在 任 何 程 序 中 都 會 存 在 一 些 變 量 有 着 相 同 的 內 部 結 構 ， 但 是 卻 表 示 完 全 不 同 的 概 念 。 例 如 ， 一 個 int類 型 的 變 量 可 以 用 來 表 示 一 個 循 環 的 迭 代 索 引 、 或 者 一 個 時 間 戳 、 或 者 一 個 文 件 描 述 符 、 或 者 一 個 月 份 ； 一 個 float64類 型 的 變 量 可 以 用 來 表 示 每 秒 移 動 幾 米 的 速 度 、 或 者 是 不 同 溫 度 單 位 下 的 溫 度 ； 一 個 字 符 串 可 以 用 來 表 示 一 個 密 碼 或 者 一 個 顔 色 的 名 稱 。 < / p >
< p > 一 個 類 型 聲 明 語 句 創 建 了 一 個 新 的 類 型 名 稱 ， 和 現 有 類 型 具 有 相 同 的 底 層 結 構 。 新 命 名 的 類 型 提 供 了 一 個 方 法 ， 用 來 分 隔 不 同 概 念 的 類 型 ， 這 樣 卽 使 它 們 底 層 類 型 相 同 也 是 不 兼 容 的 。 < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > type< / span > 類 型 名 字 底 層 類 型
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< / code > < / pre >
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< p > 類 型 聲 明 語 句 一 般 出 現 在 包 一 級 ， 因 此 如 果 新 創 建 的 類 型 名 字 的 首 字 符 大 寫 ， 則 在 外 部 包 也 可 以 使 用 。 < / p >
< p > 譯 註 ： 對 於 中 文 漢 字 ， Unicode標 誌 都 作 爲 小 寫 字 母 處 理 ， 因 此 中 文 的 命 名 默 認 不 能 導 出 ； 不 過 国 內 的 用 戶 針 對 該 問 題 提 出 了 我 們 自 己 的 間 接 ， 根 據 RobPike的 迴 複 ， 在 Go2中 有 可 能 會 將 中 日 韓 等 字 符 當 作 大 寫 字 母 處 理 。 下 面 是 RobPik在 < a href = "https://github.com/golang/go/issues/5763" target = "_blank" > Issue763< / a > 的 迴 複 ： < / p >
< blockquote >
< p > A solution that' s been kicking around for a while:< / p >
< p > For Go 2 (can' t do it before then): Change the definition to “ lower case letters and < em > are package-local; all else is exported” . Then with non-cased languages, such as Japanese, we can write 日 本 語 for an exported name and < / em > 日 本 語 for a local name. This rule has no effect, relative to the Go 1 rule, with cased languages. They behave exactly the same.< / p >
< / blockquote >
< p > 爲 了 説 明 類 型 聲 明 ， 我 們 將 不 同 溫 度 單 位 分 别 定 義 爲 不 同 的 類 型 ： < / p >
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< pre > < code class = "lang-Go" > gopl.io/ch2/tempconv0
< span class = "hljs-comment" > // Package tempconv performs Celsius and Fahrenheit temperature computations.< / span >
< span class = "hljs-keyword" > package< / span > tempconv
< span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " fmt" < / span >
< span class = "hljs-keyword" > type< / span > Celsius < span class = "hljs-typename" > float64< / span > < span class = "hljs-comment" > // 攝 氏 溫 度 < / span >
< span class = "hljs-keyword" > type< / span > Fahrenheit < span class = "hljs-typename" > float64< / span > < span class = "hljs-comment" > // 華 氏 溫 度 < / span >
< span class = "hljs-keyword" > const< / span > (
AbsoluteZeroC Celsius = -< span class = "hljs-number" > 273.15< / span > < span class = "hljs-comment" > // 絶 對 零 度 < / span >
FreezingC Celsius = < span class = "hljs-number" > 0< / span > < span class = "hljs-comment" > // 結 冰 點 溫 度 < / span >
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BoilingC Celsius = < span class = "hljs-number" > 100< / span > < span class = "hljs-comment" > // 沸 水 溫 度 < / span >
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)
< span class = "hljs-keyword" > func< / span > CToF(c Celsius) Fahrenheit { < span class = "hljs-keyword" > return< / span > Fahrenheit(c*< span class = "hljs-number" > 9< / span > /< span class = "hljs-number" > 5< / span > + < span class = "hljs-number" > 32< / span > ) }
< span class = "hljs-keyword" > func< / span > FToC(f Fahrenheit) Celsius { < span class = "hljs-keyword" > return< / span > Celsius((f - < span class = "hljs-number" > 32< / span > ) * < span class = "hljs-number" > 5< / span > / < span class = "hljs-number" > 9< / span > ) }
< / code > < / pre >
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< p > 我 們 在 這 個 包 聲 明 了 兩 種 類 型 ： Celsius和 Fahrenheit分 别 對 應 不 同 的 溫 度 單 位 。 它 們 雖 然 有 着 相 同 的 底 層 類 型 float64， 但 是 它 們 是 不 同 的 數 據 類 型 ， 因 此 它 們 不 可 以 被 相 互 比 較 或 混 在 一 個 表 達 式 運 算 。 刻 意 區 分 類 型 ， 可 以 避 免 一 些 像 無 意 中 使 用 不 同 單 位 的 溫 度 混 合 計 算 導 致 的 錯 誤 ； 因 此 需 要 一 個 類 似 Celsius(t)或 Fahrenheit(t)形 式 的 顯 式 轉 型 操 作 才 能 將 float64轉 爲 對 應 的 類 型 。 Celsius(t)和 Fahrenheit(t)是 類 型 轉 換 操 作 ， 它 們 併 不 是 函 數 調 用 。 類 型 轉 換 不 會 改 變 值 本 身 ， 但 是 會 使 它 們 的 語 義 發 生 變 化 。 另 一 方 面 ， CToF和 FToC兩 個 函 數 則 是 對 不 同 溫 度 單 位 下 的 溫 度 進 行 換 算 ， 它 們 會 返 迴 不 同 的 值 。 < / p >
< p > 對 於 每 一 個 類 型 T， 都 有 一 個 對 應 的 類 型 轉 換 操 作 T(x)， 用 於 將 x轉 爲 T類 型 （ 譯 註 ： 如 果 T是 指 針 類 型 ， 可 能 會 需 要 用 小 括 弧 包 裝 T， 比 如 < code > (*int)(0)< / code > ） 。 隻 有 當 兩 個 類 型 的 底 層 基 礎 類 型 相 同 時 ， 才 允 許 這 種 轉 型 操 作 ， 或 者 是 兩 者 都 是 指 向 相 同 底 層 結 構 的 指 針 類 型 ， 這 些 轉 換 隻 改 變 類 型 而 不 會 影 響 值 本 身 。 如 果 x是 可 以 賦 值 給 T類 型 的 值 ， 那 麽 x必 然 也 可 以 被 轉 爲 T類 型 ， 但 是 一 般 沒 有 這 個 必 要 。 < / p >
< p > 數 值 類 型 之 間 的 轉 型 也 是 允 許 的 ， 併 且 在 字 符 串 和 一 些 特 定 類 型 的 slice之 間 也 是 可 以 轉 換 的 ， 在 下 一 章 我 們 會 看 到 這 樣 的 例 子 。 這 類 轉 換 可 能 改 變 值 的 表 現 。 例 如 ， 將 一 個 浮 點 數 轉 爲 整 數 將 丟 棄 小 數 部 分 ， 將 一 個 字 符 串 轉 爲 < code > []byte< / code > 類 型 的 slice將 拷 貝 一 個 字 符 串 數 據 的 副 本 。 在 任 何 情 況 下 ， 運 行 時 不 會 發 生 轉 換 失 敗 的 錯 誤 （ 譯 註 : 錯 誤 隻 會 發 生 在 編 譯 階 段 ） 。 < / p >
< p > 底 層 數 據 類 型 決 定 了 內 部 結 構 和 表 達 方 式 ， 也 決 定 是 否 可 以 像 底 層 類 型 一 樣 對 內 置 運 算 符 的 支 持 。 這 意 味 着 ， Celsius和 Fahrenheit類 型 的 算 術 運 算 行 爲 和 底 層 的 float64類 型 是 一 樣 的 ， 正 如 我 們 所 期 望 的 那 樣 。 < / p >
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< pre > < code class = "lang-Go" > fmt.Printf(< span class = "hljs-string" > " %g\n" < / span > , BoilingC-FreezingC) < span class = "hljs-comment" > // " 100" ° C< / span >
boilingF := CToF(BoilingC)
fmt.Printf(< span class = "hljs-string" > " %g\n" < / span > , boilingF-CToF(FreezingC)) < span class = "hljs-comment" > // " 180" ° F< / span >
fmt.Printf(< span class = "hljs-string" > " %g\n" < / span > , boilingF-FreezingC) < span class = "hljs-comment" > // compile error: type mismatch< / span >
< / code > < / pre >
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< p > 比 較 運 算 符 < code > ==< / code > 和 < code > < < / code > 也 可 以 用 來 比 較 一 個 命 名 類 型 的 變 量 和 另 一 個 有 相 同 類 型 的 變 量 或 有 相 同 底 層 類 型 的 值 做 比 較 。 但 是 如 果 兩 個 值 有 着 不 同 的 類 型 ， 則 不 能 直 接 進 行 比 較 ： < / p >
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< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > var< / span > c Celsius
< span class = "hljs-keyword" > var< / span > f Fahrenheit
fmt.Println(c == < span class = "hljs-number" > 0< / span > ) < span class = "hljs-comment" > // " true" < / span >
fmt.Println(f > = < span class = "hljs-number" > 0< / span > ) < span class = "hljs-comment" > // " true" < / span >
fmt.Println(c == f) < span class = "hljs-comment" > // compile error: type mismatch< / span >
fmt.Println(c == Celsius(f)) < span class = "hljs-comment" > // " true" !< / span >
< / code > < / pre >
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< p > 註 意 最 後 那 個 語 句 。 盡 管 看 起 來 想 函 數 調 用 ， 但 是 Celsius(f)是 類 型 轉 換 操 作 ， 它 併 不 會 改 變 值 ， 僅 僅 是 改 變 值 的 類 型 而 已 。 測 試 爲 眞 的 原 因 是 因 爲 c和 g都 是 零 值 。 < / p >
< p > 一 個 命 名 的 類 型 可 以 提 供 書 寫 方 便 ， 特 别 是 可 以 避 免 一 遍 又 一 遍 地 書 寫 複 雜 類 型 （ 譯 註 ： 例 如 用 匿 名 的 結 構 體 定 義 變 量 ） 。 雖 然 對 於 像 float64這 種 簡 單 的 底 層 類 型 沒 有 簡 潔 很 多 ， 但 是 如 果 是 複 雜 的 類 型 將 會 簡 潔 很 多 ， 特 别 是 我 們 卽 將 討 論 的 結 構 體 類 型 。 < / p >
< p > 命 名 類 型 還 可 以 爲 該 類 型 的 值 定 義 新 的 行 爲 。 這 些 行 爲 表 示 爲 一 組 關 聯 到 該 類 型 的 函 數 集 合 ， 我 們 稱 爲 類 型 的 方 法 集 。 我 們 將 在 第 六 章 中 討 論 方 法 的 細 節 ， 這 里 值 説 寫 簡 單 用 法 。 < / p >
< p > 下 面 的 聲 明 語 句 ， Celsius類 型 的 參 數 c出 現 在 了 函 數 名 的 前 面 ， 表 示 聲 明 的 是 Celsius類 型 的 一 個 叫 名 叫 String的 方 法 ， 該 方 法 返 迴 該 類 型 對 象 c帶 着 ° C溫 度 單 位 的 字 符 串 ： < / p >
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< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > func< / span > (c Celsius) String() < span class = "hljs-typename" > string< / span > { < span class = "hljs-keyword" > return< / span > fmt.Sprintf(< span class = "hljs-string" > " %g° C" < / span > , c) }
< / code > < / pre >
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< p > 許 多 類 型 都 會 定 義 一 個 String方 法 ， 因 爲 當 使 用 fmt包 的 打 印 方 法 時 ， 將 會 優 先 使 用 該 類 型 對 應 的 String方 法 返 迴 的 結 果 打 印 ， 我 們 將 在 7.1節 講 述 。 < / p >
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< pre > < code class = "lang-Go" > c := FToC(< span class = "hljs-number" > 212.0< / span > )
fmt.Println(c.String()) < span class = "hljs-comment" > // " 100° C" < / span >
fmt.Printf(< span class = "hljs-string" > " %v\n" < / span > , c) < span class = "hljs-comment" > // " 100° C" ; no need to call String explicitly< / span >
fmt.Printf(< span class = "hljs-string" > " %s\n" < / span > , c) < span class = "hljs-comment" > // " 100° C" < / span >
fmt.Println(c) < span class = "hljs-comment" > // " 100° C" < / span >
fmt.Printf(< span class = "hljs-string" > " %g\n" < / span > , c) < span class = "hljs-comment" > // " 100" ; does not call String< / span >
fmt.Println(< span class = "hljs-typename" > float64< / span > (c)) < span class = "hljs-comment" > // " 100" ; does not call String< / span >
< / code > < / pre >
< / section >
< / div >
< / div >
< / div >
< a href = "../ch2/ch2-04.html" class = "navigation navigation-prev " aria-label = "Previous page: 賦值" > < i class = "fa fa-angle-left" > < / i > < / a >
< a href = "../ch2/ch2-06.html" class = "navigation navigation-next " aria-label = "Next page: 包和文件" > < 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 >
