2015-12-09 07:57:17 +00:00
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2015-12-16 02:56:29 +00:00
< div class = "book" data-level = "2.5" data-chapter-title = "類型" data-filepath = "ch2/ch2-05.md" data-basepath = ".." data-revision = "Wed Dec 16 2015 10:54:29 GMT+0800 (中国标准时间)" >
2015-12-09 07:57:17 +00:00
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前言
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< b > 0.1.< / b >
Go語言起源
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< b > 0.2.< / b >
Go語言項目
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< b > 0.3.< / b >
本書的組織
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< b > 0.4.< / b >
更多的信息
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< b > 0.5.< / b >
緻謝
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< li class = "chapter " data-level = "1" data-path = "ch1/ch1.html" >
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< b > 1.< / b >
入門
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< b > 1.1.< / b >
Hello, World
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< b > 1.2.< / b >
命令行參數
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< b > 1.3.< / b >
査找重復的行
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< b > 1.4.< / b >
GIF動畫
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< b > 1.5.< / b >
穫取URL
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< a href = "../ch1/ch1-06.html" >
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< b > 1.6.< / b >
併髮穫取多個URL
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< b > 1.7.< / b >
Web服務
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< b > 1.8.< / b >
本章要點
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< b > 2.< / b >
程序結構
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< b > 2.1.< / b >
命名
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< li class = "chapter " data-level = "2.2" data-path = "ch2/ch2-02.html" >
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< b > 2.2.< / b >
聲明
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< b > 2.3.< / b >
變量
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< b > 2.4.< / b >
賦值
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< b > 2.5.< / b >
類型
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< b > 2.6.< / b >
包和文件
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< b > 2.7.< / b >
作用域
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< b > 3.< / b >
基礎數據類型
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< b > 3.1.< / b >
整型
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< b > 3.2.< / b >
浮點數
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< b > 3.3.< / b >
復數
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< b > 3.4.< / b >
佈爾型
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< b > 3.5.< / b >
字符串
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< b > 3.6.< / b >
常量
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< b > 4.< / b >
復閤數據類型
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< b > 4.1.< / b >
數組
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< li class = "chapter " data-level = "4.2" data-path = "ch4/ch4-02.html" >
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< b > 4.2.< / b >
切片
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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 >
字典
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< b > 4.4.< / b >
結構體
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< b > 4.5.< / b >
JSON
< / a >
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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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< li class = "chapter " data-level = "5.1" data-path = "ch5/ch5-01.html" >
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< b > 5.1.< / b >
函數聲明
< / a >
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< li class = "chapter " data-level = "5.2" data-path = "ch5/ch5-02.html" >
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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" >
< 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" >
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< b > 5.10.< / b >
Recover捕穫異常
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< li class = "chapter " data-level = "6" data-path = "ch6/ch6.html" >
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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 >
基於指鍼對象的方法
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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 >
< / li >
< li class = "chapter " data-level = "6.4" data-path = "ch6/ch6-04.html" >
< a href = "../ch6/ch6-04.html" >
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< b > 6.4.< / b >
方法值和方法錶達式
< / a >
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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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< li class = "chapter " data-level = "7" data-path = "ch7/ch7.html" >
< a href = "../ch7/ch7.html" >
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< b > 7.< / b >
接口
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< li class = "chapter " data-level = "7.1" data-path = "ch7/ch7-01.html" >
< a href = "../ch7/ch7-01.html" >
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< b > 7.1.< / b >
接口是閤約
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< li class = "chapter " data-level = "7.2" data-path = "ch7/ch7-02.html" >
< a href = "../ch7/ch7-02.html" >
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< b > 7.2.< / b >
接口類型
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< li class = "chapter " data-level = "7.3" data-path = "ch7/ch7-03.html" >
< a href = "../ch7/ch7-03.html" >
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< b > 7.3.< / b >
實現接口的條件
< / a >
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< li class = "chapter " data-level = "7.4" data-path = "ch7/ch7-04.html" >
< a href = "../ch7/ch7-04.html" >
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< b > 7.4.< / b >
flag.Value接口
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< li class = "chapter " data-level = "7.5" data-path = "ch7/ch7-05.html" >
< a href = "../ch7/ch7-05.html" >
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< b > 7.5.< / b >
接口值
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< li class = "chapter " data-level = "7.6" data-path = "ch7/ch7-06.html" >
< a href = "../ch7/ch7-06.html" >
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< b > 7.6.< / b >
sort.Interface接口
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< li class = "chapter " data-level = "7.7" data-path = "ch7/ch7-07.html" >
< a href = "../ch7/ch7-07.html" >
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< b > 7.7.< / b >
http.Handler接口
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< li class = "chapter " data-level = "7.8" data-path = "ch7/ch7-08.html" >
< a href = "../ch7/ch7-08.html" >
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< b > 7.8.< / b >
error接口
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< li class = "chapter " data-level = "7.9" data-path = "ch7/ch7-09.html" >
< a href = "../ch7/ch7-09.html" >
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< b > 7.9.< / b >
示例: 錶達式求值
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< li class = "chapter " data-level = "7.10" data-path = "ch7/ch7-10.html" >
< a href = "../ch7/ch7-10.html" >
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< b > 7.10.< / b >
類型斷言
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< li class = "chapter " data-level = "7.11" data-path = "ch7/ch7-11.html" >
< a href = "../ch7/ch7-11.html" >
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< b > 7.11.< / b >
基於類型斷言識彆錯誤類型
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< li class = "chapter " data-level = "7.12" data-path = "ch7/ch7-12.html" >
< a href = "../ch7/ch7-12.html" >
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< b > 7.12.< / b >
通過類型斷言査詢接口
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< li class = "chapter " data-level = "7.13" data-path = "ch7/ch7-13.html" >
< a href = "../ch7/ch7-13.html" >
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< b > 7.13.< / b >
類型分支
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< li class = "chapter " data-level = "7.14" data-path = "ch7/ch7-14.html" >
< a href = "../ch7/ch7-14.html" >
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< b > 7.14.< / b >
示例: 基於標記的XML解碼
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< li class = "chapter " data-level = "7.15" data-path = "ch7/ch7-15.html" >
< a href = "../ch7/ch7-15.html" >
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< b > 7.15.< / b >
補充幾點
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< li class = "chapter " data-level = "8" data-path = "ch8/ch8.html" >
< a href = "../ch8/ch8.html" >
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< b > 8.< / b >
Goroutines和Channels
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< li class = "chapter " data-level = "8.1" data-path = "ch8/ch8-01.html" >
< a href = "../ch8/ch8-01.html" >
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< b > 8.1.< / b >
Goroutines
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< li class = "chapter " data-level = "8.2" data-path = "ch8/ch8-02.html" >
< a href = "../ch8/ch8-02.html" >
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< b > 8.2.< / b >
示例: 併髮的Clock服務
< / a >
< / li >
< li class = "chapter " data-level = "8.3" data-path = "ch8/ch8-03.html" >
< a href = "../ch8/ch8-03.html" >
< i class = "fa fa-check" > < / i >
< b > 8.3.< / b >
示例: 併髮的Echo服務
< / a >
< / li >
< li class = "chapter " data-level = "8.4" data-path = "ch8/ch8-04.html" >
< a href = "../ch8/ch8-04.html" >
< i class = "fa fa-check" > < / i >
< b > 8.4.< / b >
Channels
< / a >
< / li >
< li class = "chapter " data-level = "8.5" data-path = "ch8/ch8-05.html" >
< a href = "../ch8/ch8-05.html" >
< i class = "fa fa-check" > < / i >
< b > 8.5.< / b >
併行的循環
< / a >
< / li >
< li class = "chapter " data-level = "8.6" data-path = "ch8/ch8-06.html" >
< a href = "../ch8/ch8-06.html" >
< i class = "fa fa-check" > < / i >
< b > 8.6.< / b >
示例: 併髮的Web爬蟲
< / a >
< / li >
< li class = "chapter " data-level = "8.7" data-path = "ch8/ch8-07.html" >
< a href = "../ch8/ch8-07.html" >
< i class = "fa fa-check" > < / i >
< b > 8.7.< / b >
基於select的多路復用
< / a >
< / li >
< li class = "chapter " data-level = "8.8" data-path = "ch8/ch8-08.html" >
< a href = "../ch8/ch8-08.html" >
< i class = "fa fa-check" > < / i >
< b > 8.8.< / b >
示例: 併髮的字典遍歷
< / a >
< / li >
< li class = "chapter " data-level = "8.9" data-path = "ch8/ch8-09.html" >
< a href = "../ch8/ch8-09.html" >
< i class = "fa fa-check" > < / i >
< b > 8.9.< / b >
併髮的退齣
< / a >
< / li >
< li class = "chapter " data-level = "8.10" data-path = "ch8/ch8-10.html" >
< a href = "../ch8/ch8-10.html" >
< i class = "fa fa-check" > < / i >
< b > 8.10.< / b >
示例: 聊天服務
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "9" data-path = "ch9/ch9.html" >
< a href = "../ch9/ch9.html" >
< i class = "fa fa-check" > < / i >
< b > 9.< / b >
基於共享變量的併髮
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "9.1" data-path = "ch9/ch9-01.html" >
< a href = "../ch9/ch9-01.html" >
< i class = "fa fa-check" > < / i >
< b > 9.1.< / b >
競爭條件
< / a >
< / li >
< li class = "chapter " data-level = "9.2" data-path = "ch9/ch9-02.html" >
< a href = "../ch9/ch9-02.html" >
< i class = "fa fa-check" > < / i >
< b > 9.2.< / b >
sync.Mutex互斥鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.3" data-path = "ch9/ch9-03.html" >
< a href = "../ch9/ch9-03.html" >
< i class = "fa fa-check" > < / i >
< b > 9.3.< / b >
sync.RWMutex讀寫鎖
< / a >
< / li >
< li class = "chapter " data-level = "9.4" data-path = "ch9/ch9-04.html" >
< a href = "../ch9/ch9-04.html" >
< i class = "fa fa-check" > < / i >
< b > 9.4.< / b >
內存衕步
< / a >
< / li >
< li class = "chapter " data-level = "9.5" data-path = "ch9/ch9-05.html" >
< a href = "../ch9/ch9-05.html" >
< i class = "fa fa-check" > < / i >
< b > 9.5.< / b >
sync.Once初始化
< / a >
< / li >
< li class = "chapter " data-level = "9.6" data-path = "ch9/ch9-06.html" >
< a href = "../ch9/ch9-06.html" >
< i class = "fa fa-check" > < / i >
< b > 9.6.< / b >
競爭條件檢測
< / a >
< / li >
< li class = "chapter " data-level = "9.7" data-path = "ch9/ch9-07.html" >
< a href = "../ch9/ch9-07.html" >
< i class = "fa fa-check" > < / i >
< b > 9.7.< / b >
示例: 併髮的非阻塞緩存
< / a >
< / li >
< li class = "chapter " data-level = "9.8" data-path = "ch9/ch9-08.html" >
< a href = "../ch9/ch9-08.html" >
< i class = "fa fa-check" > < / i >
< b > 9.8.< / b >
Goroutines和綫程
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "10" data-path = "ch10/ch10.html" >
< a href = "../ch10/ch10.html" >
< i class = "fa fa-check" > < / i >
< b > 10.< / b >
包和工具
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "10.1" data-path = "ch10/ch10-01.html" >
< a href = "../ch10/ch10-01.html" >
< i class = "fa fa-check" > < / i >
< b > 10.1.< / b >
簡介
< / a >
< / li >
< li class = "chapter " data-level = "10.2" data-path = "ch10/ch10-02.html" >
< a href = "../ch10/ch10-02.html" >
< i class = "fa fa-check" > < / i >
< b > 10.2.< / b >
導入路徑
< / a >
< / li >
< li class = "chapter " data-level = "10.3" data-path = "ch10/ch10-03.html" >
< a href = "../ch10/ch10-03.html" >
< i class = "fa fa-check" > < / i >
< b > 10.3.< / b >
包聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.4" data-path = "ch10/ch10-04.html" >
< a href = "../ch10/ch10-04.html" >
< i class = "fa fa-check" > < / i >
< b > 10.4.< / b >
導入聲明
< / a >
< / li >
< li class = "chapter " data-level = "10.5" data-path = "ch10/ch10-05.html" >
< a href = "../ch10/ch10-05.html" >
< i class = "fa fa-check" > < / i >
< b > 10.5.< / b >
匿名導入
< / a >
< / li >
< li class = "chapter " data-level = "10.6" data-path = "ch10/ch10-06.html" >
< a href = "../ch10/ch10-06.html" >
< i class = "fa fa-check" > < / i >
< b > 10.6.< / b >
包和命名
< / a >
< / li >
< li class = "chapter " data-level = "10.7" data-path = "ch10/ch10-07.html" >
< a href = "../ch10/ch10-07.html" >
< i class = "fa fa-check" > < / i >
< b > 10.7.< / b >
工具
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "11" data-path = "ch11/ch11.html" >
< a href = "../ch11/ch11.html" >
< i class = "fa fa-check" > < / i >
< b > 11.< / b >
測試
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "11.1" data-path = "ch11/ch11-01.html" >
< a href = "../ch11/ch11-01.html" >
< i class = "fa fa-check" > < / i >
< b > 11.1.< / b >
go test
< / a >
< / li >
< li class = "chapter " data-level = "11.2" data-path = "ch11/ch11-02.html" >
< a href = "../ch11/ch11-02.html" >
< i class = "fa fa-check" > < / i >
< b > 11.2.< / b >
測試函數
< / a >
< / li >
< li class = "chapter " data-level = "11.3" data-path = "ch11/ch11-03.html" >
< a href = "../ch11/ch11-03.html" >
< i class = "fa fa-check" > < / i >
< b > 11.3.< / b >
測試覆蓋率
< / a >
< / li >
< li class = "chapter " data-level = "11.4" data-path = "ch11/ch11-04.html" >
< a href = "../ch11/ch11-04.html" >
< i class = "fa fa-check" > < / i >
< b > 11.4.< / b >
基準測試
< / a >
< / li >
< li class = "chapter " data-level = "11.5" data-path = "ch11/ch11-05.html" >
< a href = "../ch11/ch11-05.html" >
< i class = "fa fa-check" > < / i >
< b > 11.5.< / b >
剖析
< / a >
< / li >
< li class = "chapter " data-level = "11.6" data-path = "ch11/ch11-06.html" >
< a href = "../ch11/ch11-06.html" >
< i class = "fa fa-check" > < / i >
< b > 11.6.< / b >
示例函數
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "12" data-path = "ch12/ch12.html" >
< a href = "../ch12/ch12.html" >
< i class = "fa fa-check" > < / i >
< b > 12.< / b >
反射
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "12.1" data-path = "ch12/ch12-01.html" >
< a href = "../ch12/ch12-01.html" >
< i class = "fa fa-check" > < / i >
< b > 12.1.< / b >
為何需要反射?
< / a >
< / li >
< li class = "chapter " data-level = "12.2" data-path = "ch12/ch12-02.html" >
< a href = "../ch12/ch12-02.html" >
< i class = "fa fa-check" > < / i >
< b > 12.2.< / b >
reflect.Type和reflect.Value
< / a >
< / li >
< li class = "chapter " data-level = "12.3" data-path = "ch12/ch12-03.html" >
< a href = "../ch12/ch12-03.html" >
< i class = "fa fa-check" > < / i >
< b > 12.3.< / b >
Display遞歸打印
< / a >
< / li >
< li class = "chapter " data-level = "12.4" data-path = "ch12/ch12-04.html" >
< a href = "../ch12/ch12-04.html" >
< i class = "fa fa-check" > < / i >
< b > 12.4.< / b >
示例: 編碼S錶達式
< / a >
< / li >
< li class = "chapter " data-level = "12.5" data-path = "ch12/ch12-05.html" >
< a href = "../ch12/ch12-05.html" >
< i class = "fa fa-check" > < / i >
< b > 12.5.< / b >
通過reflect.Value脩改值
< / a >
< / li >
< li class = "chapter " data-level = "12.6" data-path = "ch12/ch12-06.html" >
< a href = "../ch12/ch12-06.html" >
< i class = "fa fa-check" > < / i >
< b > 12.6.< / b >
示例: 解碼S錶達式
< / a >
< / li >
< li class = "chapter " data-level = "12.7" data-path = "ch12/ch12-07.html" >
< a href = "../ch12/ch12-07.html" >
< i class = "fa fa-check" > < / i >
< b > 12.7.< / b >
穫取結構體字段標識
< / a >
< / li >
< li class = "chapter " data-level = "12.8" data-path = "ch12/ch12-08.html" >
< a href = "../ch12/ch12-08.html" >
< i class = "fa fa-check" > < / i >
< b > 12.8.< / b >
顯示一個類型的方法集
< / a >
< / li >
< li class = "chapter " data-level = "12.9" data-path = "ch12/ch12-09.html" >
< a href = "../ch12/ch12-09.html" >
< i class = "fa fa-check" > < / i >
< b > 12.9.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "13" data-path = "ch13/ch13.html" >
< a href = "../ch13/ch13.html" >
< i class = "fa fa-check" > < / i >
< b > 13.< / b >
底層編程
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "13.1" data-path = "ch13/ch13-01.html" >
< a href = "../ch13/ch13-01.html" >
< i class = "fa fa-check" > < / i >
< b > 13.1.< / b >
unsafe.Sizeof, Alignof 和 Offsetof
< / a >
< / li >
< li class = "chapter " data-level = "13.2" data-path = "ch13/ch13-02.html" >
< a href = "../ch13/ch13-02.html" >
< i class = "fa fa-check" > < / i >
< b > 13.2.< / b >
unsafe.Pointer
< / a >
< / li >
< li class = "chapter " data-level = "13.3" data-path = "ch13/ch13-03.html" >
< a href = "../ch13/ch13-03.html" >
< i class = "fa fa-check" > < / i >
< b > 13.3.< / b >
示例: 深度相等判斷
< / a >
< / li >
< li class = "chapter " data-level = "13.4" data-path = "ch13/ch13-04.html" >
< a href = "../ch13/ch13-04.html" >
< i class = "fa fa-check" > < / i >
< b > 13.4.< / b >
通過cgo調用C代碼
< / a >
< / li >
< li class = "chapter " data-level = "13.5" data-path = "ch13/ch13-05.html" >
< a href = "../ch13/ch13-05.html" >
< i class = "fa fa-check" > < / i >
< b > 13.5.< / b >
幾點忠告
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "14" data-path = "exercise/ex.html" >
< a href = "../exercise/ex.html" >
< i class = "fa fa-check" > < / i >
< b > 14.< / b >
習題解答
< / a >
< ul class = "articles" >
< li class = "chapter " data-level = "14.1" data-path = "exercise/ex-ch1.html" >
< a href = "../exercise/ex-ch1.html" >
< i class = "fa fa-check" > < / i >
< b > 14.1.< / b >
第一章 入門
< / a >
< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "15" data-path = "errata.html" >
< a href = "../errata.html" >
< i class = "fa fa-check" > < / i >
< b > 15.< / b >
勘誤
< / a >
< / li >
< li class = "divider" > < / li >
< li >
< a href = "https://www.gitbook.com" target = "blank" class = "gitbook-link" >
本書使用 GitBook 釋出
< / a >
< / li >
< / ul >
< / nav >
< / div >
< div class = "book-body" >
< div class = "body-inner" >
< div class = "book-header" role = "navigation" >
<!-- Actions Left -->
<!-- Title -->
< h1 >
< i class = "fa fa-circle-o-notch fa-spin" > < / i >
< a href = "../" > Go编程语言< / a >
< / h1 >
< / div >
< div class = "page-wrapper" tabindex = "-1" role = "main" >
< div class = "page-inner" >
< section class = "normal" id = "section-" >
< h2 id = "25-類型聲明" > 2.5. 類 型 聲 明 < / h2 >
< p > 變 量 或 錶 達 式 的 類 型 定 義 了 對 應 存 儲 值 的 特 徵 , 例 如 數 值 的 存 儲 大 小 (或 者 是 元 素 的 bit個 數 ), 它 們 在 內 部 是 如 何 錶 達 的 , 是 否 支 持 一 些 操 作 符 , 以 及 它 們 自 己 關 聯 的 方 法 集 ,< / p >
< p > 在 任 何 程 序 中 都 會 有 一 些 變 量 有 着 相 衕 的 內 部 實 現 , 但 是 錶 示 完 全 不 衕 的 概 唸 .
例 如 , int 類 型 的 變 量 可 以 用 來 錶 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 錶 示 每 秒 幾 米 的 速 度 , 或 者 是 不 衕 溫 度 單 位 的 溫 度 ;
一 個 字 符 串 可 以 用 來 錶 示 一 個 密 碼 或 者 一 個 顔 色 的 名 稱 .< / p >
< p > 一 個 類 型 的 聲 明 創 建 了 一 個 新 的 類 型 名 稱 , 和 現 有 類 型 具 有 相 衕 的 底 層 結 構 .
新 命 名 的 類 型 提 供 了 一 個 方 法 , 用 來 分 隔 不 衕 概 唸 的 類 型 , 卽 使 它 們 底 層 類 型 相 衕 也 是 不 兼 容 的 .< / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > type< / span > name underlying-< span class = "hljs-keyword" > type< / span >
< / code > < / pre >
< p > 類 型 的 聲 明 一 般 齣 現 在 包 級 彆 , 因 此 如 果 新 創 建 的 類 型 名 字 名 字 的 首 字 符 大 寫 , 則 在 外 部 包 也 可 以 使 用 .< / p >
< p > 為 了 說 明 類 型 聲 明 , 我 們 將 不 衕 溫 度 單 位 分 彆 定 義 為 不 衕 的 類 型 :< / p >
< p > 為 了 說 明 類 型 聲 明 ,讓 我 們 把 不 衕 溫 度 範 圍 分 為 不 衕 的 類 型 :< / p >
< 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 >
BoilingC Celsius = < span class = "hljs-number" > 100< / span > < span class = "hljs-comment" > // 沸 水 問 題 < / span >
)
< 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 >
< p > 這 個 包 定 義 了 兩 種 類 型 , Celsius 和 Fahrenheit 分 彆 對 應 不 衕 的 溫 度 單 位 . 它 們 都 有 着 相 衕 的 底 層 類 型 float64, 但 是 它 們 是 不 衕 的 數 據 類 型 , 因 此 它 們 不 可 以 被 相 互 比 較 或 混 在 一 個 錶 達 式 計 算 . 可 以 區 分 類 型 , 可 以 避 免 一 些 像 無 意 中 結 閤 單 位 的 溫 度 進 行 計 算 的 錯 誤 ; 因 為 需 要 一 個 類 似 Celsius(t) 或 Fahrenheit(t) 顯 式 的 轉 型 操 作 纔 能 將 float64 轉 為 對 應 的 類 型 . Celsius(t) 和 Fahrenheit(t) 是 類 型 轉 換 操 作 , 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 髮 生 變 化 . 另 一 方 麫 , 函 數 CToF 和 FToC 則 是 對 兩 個 不 衕 的 溫 度 單 位 進 行 轉 換 , 它 們 會 返 迴 不 衕 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 為 T 類 型 .
隻 有 當 兩 個 類 型 的 底 層 基 礎 類 型 相 衕 時 , 纔 允 許 這 種 轉 型 操 作 , 或 者 是 兩 者 都 是 指 曏 相 衕 底 層 結 構 的 指 鍼 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 , 那 麼 x必 然 可 以 被 轉 為 T類 型 , 但 是 一 般 沒 有 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 切 片 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 錶 現 . 例 如 , 將 一 個 浮 點 數 轉 為 整 數 將 丟 棄 小 數 部 分 , 將 一 個 字 符 串 轉 為 []byte 切 片 將 拷 貝 一 個 字 符 串 數 據 的 副 本 . 在 任 何 情 況 下 , 運 行 時 不 會 髮 送 轉 換 失 敗 的 錯 誤 (譯 註 : 錯 誤 隻 會 髮 生 在 編 譯 階 段 ).< / p >
< p > 底 層 數 據 類 型 決 定 了 內 部 結 構 和 錶 達 方 式 , 也 包 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 朮 行 為 和 底 層 的 float64 類 型 一 樣 , 正 如 你 所 期 望 的 .< / p >
< 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 >
< 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 衕 類 型 的 變 量 或 相 衕 的 底 層 類 型 的 值 做 比 較 .
但 是 如 果 兩 個 值 有 着 不 衕 的 類 型 , 則 不 能 直 接 進 行 比 較 :< / p >
< 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 >
< p > 註 意 最 後 那 個 語 句 . 盡 管 看 起 來 想 函 數 調 用 , 但 是 Celsius(f)類 型 轉 換 , 併 不 會 改 變 值 , 它 僅 僅 是 改 變 值 的 類 型 而 已 . 測 試 為 眞 的 原 因 是 因 為 c 和 g 都 是 零 值 .< / p >
< p > 一 個 命 名 的 類 型 可 以 提 供 符 號 方 便 , 特 彆 是 可 以 避 免 一 遍 又 一 遍 地 書 寫 復 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 復 雜 的 類 型 將 會 簡 潔 很 多 , 正 如 我 們 卽 將 討 論 的 結 構 體 類 型 :< / p >
< p > 命 名 類 型 還 可 以 為 該 類 型 的 值 定 義 新 的 行 為 . 這 些 行 為 錶 示 為 一 組 關 聯 到 類 型 的 函 數 , 我 們 成 為 類 型 的 方 法 集 . 我 們 將 在 第 六 章 討 論 方 法 的 細 節 , 這 裏 值 說 寫 簡 單 用 法 .< / p >
< p > 下 麫 的 聲 明 , Celsius 類 型 的 參 數 c 齣 現 在 了 函 數 名 的 前 麫 , 錶 示 聲 明 一 個 Celsius 類 型 的 名 叫 String 的 方 法 , 方 法 返 迴 帶 着 ° C 溫 度 單 位 的 參 數 c 的 數 字 打 印 字 符 串 :< / p >
< 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 >
< p > 許 多 類 型 都 會 定 義 個 String 方 法 , 因 為 當 然 用 fmt 包 的 打 印 方 法 時 , 將 會 優 先 使 用 String 方 法 返 迴 的 結 果 打 印 , 將 在 7.1節 講 述 .< / p >
< 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 >
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< script src = "../gitbook/app.js" > < / script >
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< script >
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gitbook.start(config);
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