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 = "2.2" data-chapter-title = "聲明" data-filepath = "ch2/ch2-02.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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< 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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< a href = "../ch1/ch1-05.html" >
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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 active" 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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< 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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< 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" >
< a href = "../ch5/ch5-02.html" >
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< b > 5.2.< / b >
遞歸
< / a >
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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" >
< a href = "../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" >
< a href = "../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 >
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" >
< a href = "../ch6/ch6-01.html" >
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< b > 6.1.< / b >
方法聲明
< / a >
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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
< / a >
< / li >
< 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 >
< / li >
< 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 >
< 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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< ul class = "articles" >
< 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
< / a >
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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 >
< 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 >
< 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 >
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< / 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 = "22-聲明" > 2.2. 聲 明 < / h2 >
< p > 聲 明 定 義 了 程 序 的 入 口 以 及 部 分 或 全 部 的 屬 性 . Go主 要 有 四 種 聲 明 類 型 : var, const, type, 和 func, 分 彆 對 應 變 量 , 常 量 , 類 型 , 和 函 數 的 聲 明 . 這 一 章 我 們 重 點 討 論 變 量 和 類 型 的 聲 明 , 第 三 章 將 討 論 常 量 的 聲 明 , 第 五 章 將 討 論 函 數 的 聲 明 .< / p >
< p > 一 個 Go程 序 存 儲 在 一 個 或 多 個 以 < code > .go< / code > 為 後 綴 名 的 文 件 中 . 每 個 文 件 以 個 包 的 聲 明 開 始 , 以 說 明 文 件 是 屬 於 包 的 一 部 分 .
包 聲 明 之 後 是 import 導 入 聲 明 , 然 後 是 包 一 級 的 類 型 /變 量 /常 量 /函 數 的 聲 明 , 聲 明 的 順 序 無 關 緊 要 . 例 如 , 下 麫 的 例 子 聲 明 了 一 個 常 量 , 一 個 函 數 和 兩 個 變 量 :< / p >
< pre > < code class = "lang-Go" > gopl.io/ch2/boiling
< span class = "hljs-comment" > // Boiling prints the boiling point of water.< / span >
< span class = "hljs-keyword" > package< / span > main
< span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " fmt" < / span >
< span class = "hljs-keyword" > const< / span > boilingF = < span class = "hljs-number" > 212.0< / span >
< span class = "hljs-keyword" > func< / span > main() {
< span class = "hljs-keyword" > var< / span > f = boilingF
< span class = "hljs-keyword" > var< / span > c = (f - < span class = "hljs-number" > 32< / span > ) * < span class = "hljs-number" > 5< / span > / < span class = "hljs-number" > 9< / span >
fmt.Printf(< span class = "hljs-string" > " boiling point = %g° F or %g° C\n" < / span > , f, c)
< span class = "hljs-comment" > // Output:< / span >
< span class = "hljs-comment" > // boiling point = 212° F or 100° C< / span >
}
< / code > < / pre >
< p > 其 中 常 量 < code > boilingF< / code > 是 在 包 一 級 聲 明 的 , 然 後 < code > f< / code > 和 < code > c< / code > 是 在 main 函 數 內 部 聲 明 的 . 在 包 一 級 聲 明 的 名 字 可 在 整 個 包 訪 問 , 而 不 僅 僅 在 其 聲 明 的 文 件 中 訪 問 . 相 比 之 下 , 侷 部 聲 明 的 名 字 就 隻 能 在 函 數 內 部 很 小 的 部 分 可 訪 問 .< / p >
< p > 一 個 函 數 的 聲 明 有 一 個 函 數 名 字 , 參 數 列 錶 (由 函 數 的 調 用 者 提 供 參 數 變 量 的 具 體 值 ), 一 個 可 選 的 返 迴 值 列 錶 , 和 包 含 函 數 語 句 定 義 的 函 數 體 . 如 果 函 數 沒 有 返 迴 值 , 那 麼 返 迴 值 列 錶 是 省 略 的 . 執 行 函 數 從 函 數 的 第 一 個 語 句 開 始 , 但 是 順 序 執 行 直 到 遇 到 renturn 返 迴 語 言 , 如 果 沒 有 返 迴 語 句 則 是 到 函 數 末 尾 , 然 後 返 迴 到 調 用 者 .< / p >
< p > 我 們 已 經 看 到 過 很 多 函 數 的 例 子 了 , 在 第 五 章 將 深 入 討 論 函 數 的 細 節 , 這 裏 隻 粗 略 說 下 . 下 麫 的 < code > fToC< / code > 函 數 封 裝 了 溫 度 轉 換 的 邏 輯 , 這 樣 它 隻 需 要 定 義 一 次 , 就 可 以 在 多 個 地 方 多 次 使 用 . 這 個 例 子 中 , main 函 數 就 調 用 了 兩 次 < code > fToC< / code > 函 數 , 分 彆 是 使 用 侷 部 定 義 的 兩 個 常 量 作 為 函 數 參 數 .< / p >
< pre > < code class = "lang-Go" > gopl.io/ch2/ftoc
< span class = "hljs-comment" > // Ftoc prints two Fahrenheit-to-Celsius conversions.< / span >
< span class = "hljs-keyword" > package< / span > main
< span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " fmt" < / span >
< span class = "hljs-keyword" > func< / span > main() {
< span class = "hljs-keyword" > const< / span > freezingF, boilingF = < span class = "hljs-number" > 32.0< / span > , < span class = "hljs-number" > 212.0< / span >
fmt.Printf(< span class = "hljs-string" > " %g° F = %g° C\n" < / span > , freezingF, fToC(freezingF)) < span class = "hljs-comment" > // " 32° F = 0° C" < / span >
fmt.Printf(< span class = "hljs-string" > " %g° F = %g° C\n" < / span > , boilingF, fToC(boilingF)) < span class = "hljs-comment" > // " 212° F = 100° C" < / span >
}
< span class = "hljs-keyword" > func< / span > fToC(f < span class = "hljs-typename" > float64< / span > ) < span class = "hljs-typename" > float64< / span > {
< span class = "hljs-keyword" > return< / span > (f - < span class = "hljs-number" > 32< / span > ) * < span class = "hljs-number" > 5< / span > / < span class = "hljs-number" > 9< / span >
}
< / code > < / pre >
< / section >
< / div >
< / div >
< / div >
< a href = "../ch2/ch2-01.html" class = "navigation navigation-prev " aria-label = "Previous page: 命名" > < i class = "fa fa-angle-left" > < / i > < / a >
< a href = "../ch2/ch2-03.html" class = "navigation navigation-next " aria-label = "Next page: 變量" > < i class = "fa fa-angle-right" > < / i > < / a >
< / div >
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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);
});
< / script >
< / body >
< / html >
