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2015-12-16 02:56:29 +00:00
< div class = "book" data-level = "12.2" data-chapter-title = "reflect.Type和reflect.Value" data-filepath = "ch12/ch12-02.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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本書的組織
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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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< 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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< 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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< b > 5.< / b >
函數
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< b > 5.1.< / b >
函數聲明
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< b > 5.2.< / b >
遞歸
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< b > 5.3.< / b >
多返迴值
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< b > 5.4.< / b >
錯誤
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< b > 5.5.< / b >
函數值
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< b > 5.6.< / b >
匿名函數
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< li class = "chapter " data-level = "5.7" data-path = "ch5/ch5-07.html" >
< a href = "../ch5/ch5-07.html" >
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< b > 5.7.< / b >
可變參數
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< b > 5.8.< / b >
Deferred函數
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< b > 5.9.< / b >
Panic異常
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< b > 5.10.< / b >
Recover捕穫異常
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< b > 6.< / b >
方法
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< b > 6.1.< / b >
方法聲明
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< li class = "chapter " data-level = "6.2" data-path = "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" >
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< b > 6.3.< / b >
通過嵌入結構體來擴展類型
< / a >
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< 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
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< / 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 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" >
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< b > 7.< / b >
接口
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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" >
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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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< 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" >
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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
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< li class = "chapter " data-level = "8.3" data-path = "ch8/ch8-03.html" >
< a href = "../ch8/ch8-03.html" >
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< b > 8.3.< / b >
示例: 併髮的Echo服務
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< a href = "../ch8/ch8-04.html" >
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< b > 8.4.< / b >
Channels
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< li class = "chapter " data-level = "8.5" data-path = "ch8/ch8-05.html" >
< a href = "../ch8/ch8-05.html" >
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< b > 8.5.< / b >
併行的循環
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< a href = "../ch8/ch8-06.html" >
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< b > 8.6.< / b >
示例: 併髮的Web爬蟲
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< li class = "chapter " data-level = "8.7" data-path = "ch8/ch8-07.html" >
< a href = "../ch8/ch8-07.html" >
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< b > 8.7.< / b >
基於select的多路復用
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< li class = "chapter " data-level = "8.8" data-path = "ch8/ch8-08.html" >
< a href = "../ch8/ch8-08.html" >
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< b > 8.8.< / b >
示例: 併髮的字典遍歷
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< / li >
< li class = "chapter " data-level = "8.9" data-path = "ch8/ch8-09.html" >
< a href = "../ch8/ch8-09.html" >
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< b > 8.9.< / b >
併髮的退齣
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< / 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
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< / 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
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< / 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
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< / 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
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< / 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
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< / li >
< / ul >
< / li >
< li class = "chapter " data-level = "10" data-path = "ch10/ch10.html" >
< a href = "../ch10/ch10.html" >
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< b > 10.< / b >
包和工具
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< ul class = "articles" >
< li class = "chapter " data-level = "10.1" data-path = "ch10/ch10-01.html" >
< a href = "../ch10/ch10-01.html" >
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< b > 10.1.< / b >
簡介
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< / 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
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< / 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
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< / 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" >
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< b > 10.7.< / b >
工具
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< / ul >
< / li >
< li class = "chapter " data-level = "11" data-path = "ch11/ch11.html" >
< a href = "../ch11/ch11.html" >
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< b > 11.< / b >
測試
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< ul class = "articles" >
< li class = "chapter " data-level = "11.1" data-path = "ch11/ch11-01.html" >
< a href = "../ch11/ch11-01.html" >
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< 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" >
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< 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
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< / li >
< li class = "chapter " data-level = "11.5" data-path = "ch11/ch11-05.html" >
< a href = "../ch11/ch11-05.html" >
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< 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" >
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< b > 11.6.< / b >
示例函數
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< li class = "chapter " data-level = "12" data-path = "ch12/ch12.html" >
< a href = "../ch12/ch12.html" >
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< b > 12.< / b >
反射
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< ul class = "articles" >
< li class = "chapter " data-level = "12.1" data-path = "ch12/ch12-01.html" >
< a href = "../ch12/ch12-01.html" >
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< b > 12.1.< / b >
為何需要反射?
< / a >
< / li >
< li class = "chapter active" 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< 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" >
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< b > 13.4.< / b >
通過cgo調用C代碼
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< / li >
< li class = "chapter " data-level = "13.5" data-path = "ch13/ch13-05.html" >
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< 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" >
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< b > 14.< / b >
習題解答
< / a >
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< li class = "chapter " data-level = "14.1" data-path = "exercise/ex-ch1.html" >
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< b > 14.1.< / b >
第一章 入門
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< li class = "chapter " data-level = "15" data-path = "errata.html" >
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< b > 15.< / b >
勘誤
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< li class = "divider" > < / li >
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< a href = "https://www.gitbook.com" target = "blank" class = "gitbook-link" >
本書使用 GitBook 釋出
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< h2 id = "122-reflecttype和reflectvalue" > 12.2. reflect.Type和 reflect.Value< / h2 >
2015-12-14 04:08:47 +00:00
< p > 反 射 是 由 reflect 包 提 供 支 持 . 它 定 義 了 兩 箇 重 要 的 類 型 , Type 和 Value. 一 箇 Type 錶 示 一 箇 Go類 型 . 它 是 一 箇 接 口 , 有 許 多 方 法 來 區 分 類 型 和 檢 査 它 們 的 組 件 , 例 如 一 箇 結 構 體 的 成 員 或 一 箇 函 數 的 參 數 等 . 唯 一 能 反 映 reflect.Type 實 現 的 是 接 口 的 類 型 描 述 信 息 (§ 7.5), 衕 樣 的 實 體 標 識 了 動 態 類 型 的 接 口 值 .< / p >
< p > 函 數 reflect.TypeOf 接 受 任 意 的 interface{} 類 型 , 併 返 迴 對 應 動 態 類 型 的 reflect.Type:< / p >
< pre > < code class = "lang-Go" > t := reflect.TypeOf(< span class = "hljs-number" > 3< / span > ) < span class = "hljs-comment" > // a reflect.Type< / span >
fmt.Println(t.String()) < span class = "hljs-comment" > // " int" < / span >
fmt.Println(t) < span class = "hljs-comment" > // " int" < / span >
< / code > < / pre >
< p > 其 中 TypeOf(3) 調 用 將 值 3 作 爲 interface{} 類 型 參 數 傳 入 . 迴 到 7.5節 的 將 一 箇 具 體 的 值 轉 爲 接 口 類 型 會 有 一 箇 隱 式 的 接 口 轉 換 操 作 , 它 會 創 建 一 箇 包 含 兩 箇 信 息 的 接 口 值 : 操 作 數 的 動 態 類 型 (這 裡 是 int)和 它 的 動 態 的 值 (這 裡 是 3).< / p >
< p > 因 爲 reflect.TypeOf 返 迴 的 是 一 箇 動 態 類 型 的 接 口 值 , 它 總 是 返 迴 具 體 的 類 型 . 因 此 , 下 麫 的 代 碼 將 打 印 " *os.File" 而 不 是 " io.Writer" . 稍 後 , 我 們 將 看 到 reflect.Type 是 具 有 識 別 接 口 類 型 的 錶 達 方 式 功 能 的 .< / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > var< / span > w io.Writer = os.Stdout
fmt.Println(reflect.TypeOf(w)) < span class = "hljs-comment" > // " *os.File" < / span >
< / code > < / pre >
< p > 要 註 意 的 是 reflect.Type 接 口 是 滿 足 fmt.Stringer 接 口 的 . 因 爲 打 印 動 態 類 型 值 對 於 調 試 和 日 誌 是 有 幫 助 的 , fmt.Printf 提 供 了 一 箇 簡 短 的 %T 標 誌 參 數 , 內 部 使 用 reflect.TypeOf 的 結 果 輸 齣 :< / p >
< pre > < code class = "lang-Go" > fmt.Printf(< span class = "hljs-string" > " %T\n" < / span > , < span class = "hljs-number" > 3< / span > ) < span class = "hljs-comment" > // " int" < / span >
< / code > < / pre >
< p > reflect 包 中 另 一 箇 重 要 的 類 型 是 Value. 一 箇 reflect.Value 可 以 持 有 一 箇 任 意 類 型 的 值 . 函 數 reflect.ValueOf 接 受 任 意 的 interface{} 類 型 , 併 返 迴 對 應 動 態 類 型 的 reflect.Value. 和 reflect.TypeOf 類 似 , reflect.ValueOf 返 迴 的 結 果 也 是 對 於 具 體 的 類 型 , 但 是 reflect.Value 也 可 以 持 有 一 箇 接 口 值 .< / p >
< pre > < code class = "lang-Go" > v := reflect.ValueOf(< span class = "hljs-number" > 3< / span > ) < span class = "hljs-comment" > // a reflect.Value< / span >
fmt.Println(v) < span class = "hljs-comment" > // " 3" < / span >
fmt.Printf(< span class = "hljs-string" > " %v\n" < / span > , v) < span class = "hljs-comment" > // " 3" < / span >
fmt.Println(v.String()) < span class = "hljs-comment" > // < span class = "hljs-doctag" > NOTE:< / span > " < int Value> " < / span >
< / code > < / pre >
< p > 和 reflect.Type 類 似 , reflect.Value 也 滿 足 fmt.Stringer 接 口 , 但 是 除 非 Value 持 有 的 是 字 符 串 , 否 則 String 隻 是 返 迴 具 體 的 類 型 . 相 衕 , 使 用 fmt 包 的 %v 標 誌 參 數 , 將 使 用 reflect.Values 的 結 果 格 式 化 .< / p >
< p > 調 用 Value 的 Type 方 法 將 返 迴 具 體 類 型 所 對 應 的 reflect.Type:< / p >
< pre > < code class = "lang-Go" > t := v.Type() < span class = "hljs-comment" > // a reflect.Type< / span >
fmt.Println(t.String()) < span class = "hljs-comment" > // " int" < / span >
< / code > < / pre >
< p > 逆 操 作 是 調 用 reflect.ValueOf 對 應 的 reflect.Value.Interface 方 法 . 它 返 迴 一 箇 interface{} 類 型 錶 示 reflect.Value 對 應 類 型 的 具 體 值 :< / p >
< pre > < code class = "lang-Go" > v := reflect.ValueOf(< span class = "hljs-number" > 3< / span > ) < span class = "hljs-comment" > // a reflect.Value< / span >
x := v.Interface() < span class = "hljs-comment" > // an interface{}< / span >
i := x.(< span class = "hljs-typename" > int< / span > ) < span class = "hljs-comment" > // an int< / span >
fmt.Printf(< span class = "hljs-string" > " %d\n" < / span > , i) < span class = "hljs-comment" > // " 3" < / span >
< / code > < / pre >
< p > 一 箇 reflect.Value 和 interface{} 都 能 保 存 任 意 的 值 . 所 不 衕 的 是 , 一 箇 空 的 接 口 隱 藏 了 值 對 應 的 錶 示 方 式 和 所 有 的 公 開 的 方 法 , 因 此 隻 有 我 們 知 道 具 體 的 動 態 類 型 纔 能 使 用 類 型 斷 言 來 訪 問 內 部 的 值 (就 像 上 麫 那 樣 ), 對 於 內 部 值 併 沒 有 特 別 可 做 的 事 情 . 相 比 之 下 , 一 箇 Value 則 有 很 多 方 法 來 檢 査 其 內 容 , 無 論 它 的 具 體 類 型 是 什 麼 . 讓 我 們 再 次 嘗 試 實 現 我 們 的 格 式 化 函 數 format.Any.< / p >
< p > 我 們 使 用 reflect.Value 的 Kind 方 法 來 替 代 之 前 的 類 型 switch. 雖 然 還 是 有 無 窮 多 的 類 型 , 但 是 它 們 的 kinds類 型 卻 是 有 限 的 : Bool, String 和 所 有 數 字 類 型 的 基 礎 類 型 ; Array 和 Struct 對 應 的 聚 閤 類 型 ; Chan, Func, Ptr, Slice, 和 Map 對 應 的 引 用 類 似 ; 接 口 類 型 ; 還 有 錶 示 空 值 的 無 效 類 型 . (空 的 reflect.Value 對 應 Invalid 無 效 類 型 .)< / p >
< pre > < code class = "lang-Go" > gopl.io/ch12/format
< span class = "hljs-keyword" > package< / span > format
< span class = "hljs-keyword" > import< / span > (
< span class = "hljs-string" > " reflect" < / span >
< span class = "hljs-string" > " strconv" < / span >
)
< span class = "hljs-comment" > // Any formats any value as a string.< / span >
< span class = "hljs-keyword" > func< / span > Any(value < span class = "hljs-keyword" > interface< / span > {}) < span class = "hljs-typename" > string< / span > {
< span class = "hljs-keyword" > return< / span > formatAtom(reflect.ValueOf(value))
}
< span class = "hljs-comment" > // formatAtom formats a value without inspecting its internal structure.< / span >
< span class = "hljs-keyword" > func< / span > formatAtom(v reflect.Value) < span class = "hljs-typename" > string< / span > {
< span class = "hljs-keyword" > switch< / span > v.Kind() {
< span class = "hljs-keyword" > case< / span > reflect.Invalid:
< span class = "hljs-keyword" > return< / span > < span class = "hljs-string" > " invalid" < / span >
< span class = "hljs-keyword" > case< / span > reflect.Int, reflect.Int8, reflect.Int16,
reflect.Int32, reflect.Int64:
< span class = "hljs-keyword" > return< / span > strconv.FormatInt(v.Int(), < span class = "hljs-number" > 10< / span > )
< span class = "hljs-keyword" > case< / span > reflect.Uint, reflect.Uint8, reflect.Uint16,
reflect.Uint32, reflect.Uint64, reflect.Uintptr:
< span class = "hljs-keyword" > return< / span > strconv.FormatUint(v.Uint(), < span class = "hljs-number" > 10< / span > )
< span class = "hljs-comment" > // ...floating-point and complex cases omitted for brevity...< / span >
< span class = "hljs-keyword" > case< / span > reflect.Bool:
< span class = "hljs-keyword" > return< / span > strconv.FormatBool(v.Bool())
< span class = "hljs-keyword" > case< / span > reflect.String:
< span class = "hljs-keyword" > return< / span > strconv.Quote(v.String())
< span class = "hljs-keyword" > case< / span > reflect.Chan, reflect.Func, reflect.Ptr, reflect.Slice, reflect.Map:
< span class = "hljs-keyword" > return< / span > v.Type().String() + < span class = "hljs-string" > " 0x" < / span > +
strconv.FormatUint(< span class = "hljs-typename" > uint64< / span > (v.Pointer()), < span class = "hljs-number" > 16< / span > )
< span class = "hljs-keyword" > default< / span > : < span class = "hljs-comment" > // reflect.Array, reflect.Struct, reflect.Interface< / span >
< span class = "hljs-keyword" > return< / span > v.Type().String() + < span class = "hljs-string" > " value" < / span >
}
}
< / code > < / pre >
< p > 到 目 前 未 知 , 我 們 的 函 數 將 每 箇 值 視 作 一 箇 不 可 分 割 沒 有 內 部 結 構 的 , 因 此 它 叫 formatAtom. 對 於 聚 閤 類 型 (結 構 體 和 數 組 )箇 接 口 隻 是 打 印 類 型 的 值 , 對 於 引 用 類 型 (channels, functions, pointers, slices, 和 maps), 它 十 六 進 製 打 印 類 型 的 引 用 地 址 . 雖 然 還 不 夠 理 想 , 但 是 依 然 是 一 箇 重 大 的 進 步 , 併 且 Kind 隻 關 心 底 層 錶 示 , format.Any 也 支 持 新 命 名 的 類 型 . 例 如 :< / p >
< pre > < code class = "lang-Go" > < span class = "hljs-keyword" > var< / span > x < span class = "hljs-typename" > int64< / span > = < span class = "hljs-number" > 1< / span >
< span class = "hljs-keyword" > var< / span > d time.Duration = < span class = "hljs-number" > 1< / span > * time.Nanosecond
fmt.Println(format.Any(x)) < span class = "hljs-comment" > // " 1" < / span >
fmt.Println(format.Any(d)) < span class = "hljs-comment" > // " 1" < / span >
fmt.Println(format.Any([]< span class = "hljs-typename" > int64< / span > {x})) < span class = "hljs-comment" > // " []int64 0x8202b87b0" < / span >
fmt.Println(format.Any([]time.Duration{d})) < span class = "hljs-comment" > // " []time.Duration 0x8202b87e0" < / span >
< / code > < / pre >
2015-12-09 07:57:17 +00:00
< / section >
< / div >
< / div >
< / div >
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< / 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);
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< / script >
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