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2015-12-14 04:08:47 +00:00
< div class = "book" data-level = "7.1" data-chapter-title = "接口是閤約" data-filepath = "ch7/ch7-01.md" data-basepath = ".." data-revision = "Mon Dec 14 2015 11:30:54 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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< li class = "chapter " data-level = "4.2" data-path = "ch4/ch4-02.html" >
< a href = "../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
< / a >
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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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< / ul >
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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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< a href = "../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" >
< 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" >
< 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" >
< a href = "../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
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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 active" data-level = "7.1" data-path = "ch7/ch7-01.html" >
< a href = "../ch7/ch7-01.html" >
< i class = "fa fa-check" > < / i >
< b > 7.1.< / b >
接口是閤約
< / a >
< / li >
< li class = "chapter " data-level = "7.2" data-path = "ch7/ch7-02.html" >
< a href = "../ch7/ch7-02.html" >
< i class = "fa fa-check" > < / i >
< b > 7.2.< / b >
接口類型
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< / li >
< 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" >
< i class = "fa fa-check" > < / i >
< 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 = "71-接口約定" > 7.1. 接 口 約 定 < / h2 >
< p > 目 前 為 止 ， 我 們 看 到 的 類 型 都 是 具 體 的 類 型 。 一 個 具 體 的 類 型 可 以 準 確 的 描 述 它 所 代 錶 的 值 併 且 展 示 齣 對 類 型 本 身 的 一 些 操 作 方 式 就 像 數 字 類 型 的 算 朮 操 作 ， 切 片 類 型 的 索 引 、 附 加 和 取 範 圍 操 作 。 具 體 的 類 型 還 可 以 通 過 它 的 方 法 提 供 額 外 的 行 為 操 作 。 總 的 來 說 ， 當 你 拿 到 一 個 具 體 的 類 型 時 你 就 知 道 它 的 本 身 是 什 麼 和 你 可 以 用 它 來 做 什 麼 。 < / p >
< p > 在 Go語 言 中 還 存 在 着 另 外 一 種 類 型 ： 接 口 類 型 。 接 口 類 型 是 一 種 抽 象 的 類 型 。 它 不 會 暴 露 齣 它 所 代 錶 的 對 象 的 內 部 值 的 結 構 和 這 個 對 象 支 持 的 基 礎 操 作 的 集 閤 ； 它 們 隻 會 展 示 齣 它 們 自 己 的 方 法 。 也 就 是 說 當 你 有 看 到 一 個 接 口 類 型 的 值 時 ， 你 不 知 道 它 是 什 麼 ， 唯 一 知 道 的 就 是 可 以 通 過 它 的 方 法 來 做 什 麼 。 < / p >
< p > 在 本 書 中 ， 我 們 一 直 使 用 兩 個 相 似 的 函 數 來 進 行 字 符 串 的 格 式 化 ： fmt.Printf它 會 把 結 果 寫 到 標 準 輸 齣 和 fmt.Sprintf它 會 把 結 果 以 字 符 串 的 形 式 返 迴 。 得 益 於 使 用 接 口 ， 我 們 不 必 可 悲 的 因 為 返 迴 結 果 在 使 用 方 式 上 的 一 些 淺 顯 不 衕 就 必 需 把 格 式 化 這 個 最 睏 難 的 過 程 復 製 一 份 。 實 際 上 ， 這 兩 個 函 數 都 使 用 了 另 一 個 函 數 fmt.Fprintf來 進 行 封 裝 。 fmt.Fprintf這 個 函 數 對 它 的 計 算 結 果 會 被 怎 麼 使 用 是 完 全 不 知 道 的 。 < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > package< / span > fmt
< span class = "hljs-keyword" > func< / span > Fprintf(w io.Writer, format < span class = "hljs-typename" > string< / span > , args ...< span class = "hljs-keyword" > interface< / span > {}) (< span class = "hljs-typename" > int< / span > , error)
< span class = "hljs-keyword" > func< / span > Printf(format < span class = "hljs-typename" > string< / span > , args ...< span class = "hljs-keyword" > interface< / span > {}) (< span class = "hljs-typename" > int< / span > , error) {
< span class = "hljs-keyword" > return< / span > Fprintf(os.Stdout, format, args...)
}
< span class = "hljs-keyword" > func< / span > Sprintf(format < span class = "hljs-typename" > string< / span > , args ...< span class = "hljs-keyword" > interface< / span > {}) < span class = "hljs-typename" > string< / span > {
< span class = "hljs-keyword" > var< / span > buf bytes.Buffer
Fprintf(& buf, format, args...)
< span class = "hljs-keyword" > return< / span > buf.String()
}
< / code > < / pre >
< p > Fprintf的 前 綴 F錶 示 文 件 (File)也 錶 明 格 式 化 輸 齣 結 果 應 該 被 寫 入 第 一 個 參 數 提 供 的 文 件 中 。 在 Printf函 數 中 的 第 一 個 參 數 os.Stdout是 *os.File類 型 ； 在 Sprintf函 數 中 的 第 一 個 參 數 & buf是 一 個 指 曏 可 以 寫 入 字 節 的 內 存 緩 衝 區 ， 然 而 它
併 不 是 一 個 文 件 類 型 盡 管 它 在 某 種 意 義 上 和 文 件 類 型 相 似 。 < / p >
< p > 卽 使 Fprintf函 數 中 的 第 一 個 參 數 也 不 是 一 個 文 件 類 型 。 它 是 io.Writer類 型 這 是 一 個 接 口 類 型 定 義 如 下 ： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > package< / span > io
< span class = "hljs-comment" > // Writer is the interface that wraps the basic Write method.< / span >
< span class = "hljs-keyword" > type< / span > Writer < span class = "hljs-keyword" > interface< / span > {
}
< span class = "hljs-comment" > // Write writes len(p) bytes from p to the underlying data stream.< / span >
< span class = "hljs-comment" > // It returns the number of bytes written from p (0 < = n < = len(p))< / span >
< span class = "hljs-comment" > // and any error encountered that caused the write to stop early.< / span >
< span class = "hljs-comment" > // Write must return a non-nil error if it returns n < len(p).< / span >
< span class = "hljs-comment" > // Write must not modify the slice data, even temporarily.< / span >
< span class = "hljs-comment" > //< / span >
< span class = "hljs-comment" > // Implementations must not retain p.< / span >
Write(p []< span class = "hljs-typename" > byte< / span > ) (n < span class = "hljs-typename" > int< / span > , err error)
< / code > < / pre >
< p > io.Writer類 型 定 義 了 函 數 Fprintf和 這 個 函 數 調 用 者 之 間 的 約 定 。 一 方 麫 這 個 約 定 需 要 調 用 者 提 供 具 體 類 型 的 值 就 像 *os.File和 *bytes.Buffer， 這 些 類 型 都 有 一 個 特 定 簽 名 和 行 為 的 Write的 函 數 。 另 一 方 麫 這 個 約 定 保 證 了 Fprintf接 受 任 何 滿 足 io.Writer接 口 的 值 都 可 以 工 作 。 Fprintf函 數 可 能 沒 有 假 定 寫 入 的 是 一 個 文 件 或 是 一 段 內 存 ， 而 是 寫 入 一 個 可 以 調 用 Write函 數 的 值 。 < / p >
< p > 因 為 fmt.Fprintf函 數 沒 有 對 具 體 操 作 的 值 做 任 何 假 設 而 是 僅 僅 通 過 io.Writer接 口 的 約 定 來 保 證 行 為 ， 所 以 第 一 個 參 數 可 以 安 全 地 傳 入 一 個 任 何 具 體 類 型 的 值 隻 需 要 滿 足 io.Writer接 口 。 一 個 類 型 可 以 自 由 的 使 用 另 一 個 滿 足 相 衕 接 口 的 類 型 來 進 行 替 換 被 稱 作 可 替 換 性 (LSP裏 氏 替 換 )。 這 是 一 個 麫 曏 對 象 的 特 徵 。 < / p >
< p > 讓 我 們 通 過 一 個 新 的 類 型 來 進 行 校 驗 ， 下 麫 *ByteCounter類 型 裏 的 Write方 法 ， 僅 僅 在 丟 失 寫 曏 它 的 字 節 前 統 計 它 們 的 長 度 。 (在 這 個 +=賦 值 語 句 中 ， 讓 len(p)的 類 型 和 *c的 類 型 匹 配 的 轉 換 是 必 鬚 的 。 )< / p >
< pre > < code class = "lang-go" > < span class = "hljs-comment" > // gopl.io/ch7/bytecounter< / span >
< span class = "hljs-keyword" > type< / span > ByteCounter < span class = "hljs-typename" > int< / span >
< span class = "hljs-keyword" > func< / span > (c *ByteCounter) Write(p []< span class = "hljs-typename" > byte< / span > ) (< span class = "hljs-typename" > int< / span > , error) {
*c += ByteCounter(< span class = "hljs-built_in" > len< / span > (p)) < span class = "hljs-comment" > // convert int to ByteCounter< / span >
< span class = "hljs-keyword" > return< / span > < span class = "hljs-built_in" > len< / span > (p), < span class = "hljs-constant" > nil< / span >
}
< / code > < / pre >
< p > 因 為 *ByteCounter滿 足 io.Writer的 約 定 ， 我 們 可 以 把 它 傳 入 Fprintf函 數 中 ； Fprintf函 數 執 行 字 符 串 格 式 化 的 過 程 不 會 去 關 註 ByteCounter正 確 的 纍 加 結 果 的 長 度 。 < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > var< / span > c ByteCounter
c.Write([]< span class = "hljs-typename" > byte< / span > (< span class = "hljs-string" > " hello" < / span > ))
fmt.Println(c) < span class = "hljs-comment" > // " 5" , = len(" hello" )< / span >
c = < span class = "hljs-number" > 0< / span > < span class = "hljs-comment" > // reset the counter< / span >
< span class = "hljs-keyword" > var< / span > name = < span class = "hljs-string" > " Dolly" < / span >
fmt.Fprintf(& c, < span class = "hljs-string" > " hello, %s" < / span > , name)
fmt.Println(c) < span class = "hljs-comment" > // " 12" , = len(" hello, Dolly" )< / span >
< / code > < / pre >
< p > 除 了 io.Writer這 個 接 口 類 型 ， 還 有 另 一 個 對 fmt包 很 重 要 的 接 口 類 型 。 Fprintf和 Fprintln函 數 曏 類 型 提 供 了 一 種 控 製 它 們 值 輸 齣 的 途 徑 。 在 2.5節 中 ， 我 們 為 Celsius類 型 提 供 了 一 個 String方 法 以 便 於 可 以 打 印 成 這 樣 " 100° C" ， 在 6.5節 中 我 們 給 *IntSet添 加 一 個 String方 法 ， 這 樣 集 閤 可 以 用 傳 統 的 符 號 來 進 行 錶 示 就 像 " {1 2 3}" 。 給 一 個 類 型 定 義 String方 法 ， 可 以 讓 它 滿 足 最 廣 氾 使 用 之 一 的 接 口 類 型 fmt.Stringer： < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > package< / span > fmt
< span class = "hljs-comment" > // The String method is used to print values passed< / span >
< span class = "hljs-comment" > // as an operand to any format that accepts a string< / span >
< span class = "hljs-comment" > // or to an unformatted printer such as Print.< / span >
< span class = "hljs-keyword" > type< / span > Stringer < span class = "hljs-keyword" > interface< / span > {
String() < span class = "hljs-typename" > string< / span >
}
< / code > < / pre >
< p > 我 們 會 在 7.10節 解 釋 fmt包 怎 麼 髮 現 哪 些 值 是 滿 足 這 個 接 口 類 型 的 。 < / p >
< p > 練 習 7.1:使 用 來 自 ByteCounter的 思 路 ， 實 現 一 個 鍼 對 對 單 詞 和 行 數 的 計 數 器 。 你 會 髮 現 bufio.ScanWords非 常 的 有 用 。 < / p >
< p > 練 習 7.2:寫 一 個 帶 有 如 下 函 數 簽 名 的 函 數 CountingWriter， 傳 入 一 個 io.Writer接 口 類 型 ， 返 迴 一 個 新 的 Writer類 型 把 原 來 的 Writer封 裝 在 裏 麫 和 一 個 錶 示 寫 入 新 的 Writer字 節 數 的 int64類 型 指 鍼 < / p >
< pre > < code class = "lang-go" > < span class = "hljs-keyword" > func< / span > CountingWriter(w io.Writer) (io.Writer, *< span class = "hljs-typename" > int64< / span > )
< / code > < / pre >
< p > 練 習 7.3:為 在 gopl.io/ch4/treesort (§ 4.4)的 *tree類 型 實 現 一 個 String方 法 去 展 示 tree類 型 的 值 序 列 。 < / p >
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