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 = "6.1" data-chapter-title = "方法聲明" data-filepath = "ch6/ch6-01.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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< b > 1.5.< / b >
穫取URL
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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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< 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
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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
< / 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
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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 active" 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
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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 >
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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 >
< / 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
< / a >
< / 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 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 = "61-方法聲明" > 6.1. 方 法 聲 明 < / h2 >
< p > 在 函 數 聲 明 時 ， 在 其 名 字 之 前 放 上 一 個 變 量 ， 卽 是 一 個 方 法 。 這 個 附 加 的 參 數 會 將 該 函 數 附 加 到 這 種 類 型 上 ， 卽 相 當 於 為 這 種 類 型 定 義 了 一 個 獨 佔 的 方 法 。 < / p >
< p > 下 麫 來 寫 我 們 第 一 個 方 法 的 例 子 ， 這 個 例 子 在 package geometry下 ： < / p >
< pre > < code class = "lang-go" > gopl.io/ch6/geometry
< span class = "hljs-keyword" > package< / span > geometry
< span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " math" < / span >
< span class = "hljs-keyword" > type< / span > Point < span class = "hljs-keyword" > struct< / span > { X, Y < span class = "hljs-typename" > float64< / span > }
< span class = "hljs-comment" > // traditional function< / span >
< span class = "hljs-keyword" > func< / span > Distance(p, q Point) < span class = "hljs-typename" > float64< / span > {
< span class = "hljs-keyword" > return< / span > math.Hypot(q.X-p.X, q.Y-p.Y)
}
< span class = "hljs-comment" > // same thing, but as a method of the Point type< / span >
< span class = "hljs-keyword" > func< / span > (p Point) Distance(q Point) < span class = "hljs-typename" > float64< / span > {
< span class = "hljs-keyword" > return< / span > math.Hypot(q.X-p.X, q.Y-p.Y)
}
< / code > < / pre >
< p > 上 麫 的 代 碼 裏 那 個 附 加 的 參 數 p， 叫 做 方 法 的 接 收 器 (receiver)， 早 期 的 麫 曏 對 象 語 言 留 下 的 遺 產 將 調 用 一 個 方 法 稱 為 “ 曏 一 個 對 象 髮 送 消 息 ” 。 < / p >
< p > 在 Go語 言 中 ， 我 們 併 不 會 像 其 它 語 言 那 樣 用 this或 者 self作 為 接 收 器 ； 我 們 可 以 任 意 的 選 擇 接 收 器 的 名 字 。 由 於 接 收 器 的 名 字 經 常 會 被 使 用 到 ， 所 以 保 持 其 在 方 法 間 傳 遞 時 的 一 緻 性 和 簡 短 性 是 不 錯 的 主 意 。 這 裏 的 建 議 是 可 以 使 用 其 類 型 的 第 一 個 字 母 ， 比 如 這 裏 使 用 了 Point的 首 字 母 p。 < / p >
< p > 在 方 法 調 用 過 程 中 ， 接 收 器 參 數 一 般 會 在 方 法 名 之 前 齣 現 。 這 和 方 法 聲 明 是 一 樣 的 ， 都 是 接 收 器 參 數 在 方 法 名 字 之 前 。 下 麫 是 例 子 ： < / p >
< pre > < code class = "lang-Go" > p := Point{< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 2< / span > }
q := Point{< span class = "hljs-number" > 4< / span > , < span class = "hljs-number" > 6< / span > }
fmt.Println(Distance(p, q)) < span class = "hljs-comment" > // " 5" , function call< / span >
fmt.Println(p.Distance(q)) < span class = "hljs-comment" > // " 5" , method call< / span >
< / code > < / pre >
< p > 可 以 看 到 ， 上 麫 的 兩 個 函 數 調 用 都 是 Distance， 但 是 卻 沒 有 髮 生 衝 突 。 第 一 個 Distance的 調 用 實 際 上 用 的 是 包 級 彆 的 函 數 geometry.Distance， 而 第 二 個 則 是 使 用 剛 剛 聲 明 的 Point， 調 用 的 是 Point類 下 聲 明 的 Point.Distance方 法 。 < / p >
< p > 這 種 p.Distance的 錶 達 式 叫 做 選 擇 器 ， 因 為 他 會 選 擇 閤 適 的 對 應 p這 個 對 象 的 Distance方 法 來 執 行 。 選 擇 器 也 會 被 用 來 選 擇 一 個 struct類 型 的 字 段 ， 比 如 p.X。 由 於 方 法 和 字 段 都 是 在 衕 一 命 名 空 間 ， 所 以 如 果 我 們 在 這 裏 聲 明 一 個 X方 法 的 話 ， 編 譯 器 會 報 錯 ， 因 為 在 調 用 p.X時 會 有 歧 義 (譯 註 ： 這 裏 確 實 挺 奇 怪 的 )。 < / p >
< p > 因 為 每 種 類 型 都 有 其 方 法 的 命 名 空 間 ， 我 們 在 用 Distance這 個 名 字 的 時 候 ， 不 衕 的 Distance調 用 指 曏 了 不 衕 類 型 裏 的 Distance方 法 。 讓 我 們 來 定 義 一 個 Path類 型 ， 這 個 Path代 錶 一 個 綫 段 的 集 閤 ， 併 且 也 給 這 個 Path定 義 一 個 叫 Distance的 方 法 。 < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-comment" > // A Path is a journey connecting the points with straight lines.< / span >
< span class = "hljs-keyword" > type< / span > Path []Point
< span class = "hljs-comment" > // Distance returns the distance traveled along the path.< / span >
< span class = "hljs-keyword" > func< / span > (path Path) Distance() < span class = "hljs-typename" > float64< / span > {
sum := < span class = "hljs-number" > 0.0< / span >
< span class = "hljs-keyword" > for< / span > i := < span class = "hljs-keyword" > range< / span > path {
< span class = "hljs-keyword" > if< / span > i > < span class = "hljs-number" > 0< / span > {
sum += path[i-< span class = "hljs-number" > 1< / span > ].Distance(path[i])
}
}
< span class = "hljs-keyword" > return< / span > sum
}
< / code > < / pre >
< p > Path是 一 個 命 名 的 slice類 型 ， 而 不 是 Point那 樣 的 struct類 型 ， 然 而 我 們 依 然 可 以 為 它 定 義 方 法 。 在 能 夠 給 任 意 類 型 定 義 方 法 這 一 點 上 ， Go和 很 多 其 它 的 麫 曏 對 象 的 語 言 不 太 一 樣 。 因 此 在 Go語 言 裏 ， 我 們 為 一 些 簡 單 的 數 值 、 字 符 串 、 slice、 map來 定 義 一 些 附 加 行 為 很 方 便 。 方 法 可 以 被 聲 明 到 任 意 類 型 ， 隻 要 不 是 一 個 指 鍼 或 者 一 個 interface。 < / p >
< p > 兩 個 Distance方 法 有 不 衕 的 類 型 。 他 們 兩 個 方 法 之 間 沒 有 任 何 關 繫 ， 盡 管 Path的 Distance方 法 會 在 內 部 調 用 Point.Distance方 法 來 計 算 每 個 連 接 鄰 接 點 的 綫 段 的 長 度 。 < / p >
< p > 讓 我 們 來 調 用 一 個 新 方 法 ， 計 算 三 角 形 的 週 長 ： < / p >
< pre > < code class = "lang-Go" > perim := Path{
{< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 1< / span > },
{< span class = "hljs-number" > 5< / span > , < span class = "hljs-number" > 1< / span > },
{< span class = "hljs-number" > 5< / span > , < span class = "hljs-number" > 4< / span > },
{< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 1< / span > },
}
fmt.Println(perim.Distance()) < span class = "hljs-comment" > // " 12" < / span >
< / code > < / pre >
< p > 在 上 麫 兩 個 對 Distance名 字 的 方 法 的 調 用 中 ， 編 譯 器 會 根 據 方 法 的 名 字 以 及 接 收 器 來 決 定 具 體 調 用 的 是 哪 一 個 函 數 。 第 一 個 例 子 中 path[i-1]數 組 中 的 類 型 是 Point， 因 此 Point.Distance這 個 方 法 被 調 用 ； 在 第 二 個 例 子 中 perim的 類 型 是 Path， 因 此 Distance調 用 的 是 Path.Distance。 < / p >
< p > 對 於 一 個 給 定 的 類 型 ， 其 內 部 的 方 法 都 必 鬚 有 唯 一 的 方 法 名 ， 但 是 不 衕 的 類 型 卻 可 以 有 衕 樣 的 方 法 名 ， 比 如 我 們 這 裏 Point和 Path就 都 有 Distance這 個 名 字 的 方 法 ； 所 以 我 們 沒 有 必 要 非 在 方 法 名 之 前 加 類 型 名 來 消 除 歧 義 ， 比 如 PathDistance。 這 裏 我 們 已 經 看 到 了 方 法 比 之 函 數 的 一 些 好 處 ： 方 法 名 可 以 簡 短 。 當 我 們 在 包 外 調 用 的 時 候 這 種 好 處 就 會 被 放 大 ， 因 為 我 們 可 以 使 用 這 個 短 名 字 ， 而 可 以 省 略 掉 包 的 名 字 ， 下 麫 是 例 子 ： < / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > import< / span > < span class = "hljs-string" > " gopl.io/ch6/geometry" < / span >
perim := geometry.Path{{< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 1< / span > }, {< span class = "hljs-number" > 5< / span > , < span class = "hljs-number" > 1< / span > }, {< span class = "hljs-number" > 5< / span > , < span class = "hljs-number" > 4< / span > }, {< span class = "hljs-number" > 1< / span > , < span class = "hljs-number" > 1< / span > }}
fmt.Println(geometry.PathDistance(perim)) < span class = "hljs-comment" > // " 12" , standalone function< / span >
fmt.Println(perim.Distance()) < span class = "hljs-comment" > // " 12" , method of geometry.Path< / span >
< / code > < / pre >
< p > 譯 註 ： 如 果 我 們 要 用 方 法 去 計 算 perim的 distance， 還 需 要 去 寫 全 geometry的 包 名 ， 和 其 函 數 名 ， 但 是 因 為 Path這 個 變 量 定 義 了 一 個 可 以 直 接 用 的 Distance方 法 ， 所 以 我 們 可 以 直 接 寫 perim.Distance()。 相 當 於 可 以 少 打 很 多 字 ， 作 者 應 該 是 這 個 意 思 。 因 為 在 Go裏 包 外 調 用 函 數 需 要 帶 上 包 名 ， 還 是 挺 麻 煩 的 。 < / p >
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