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<div class="book" data-level="2.7" data-chapter-title="作用域" data-filepath="ch2/ch2-07.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
<div class="book-summary">
<nav role="navigation">
<ul class="summary">
<li class="chapter " data-level="0" data-path="index.html">
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前言
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<ul class="articles">
<li class="chapter " data-level="0.1" data-path="ch0/ch0-01.html">
<a href="../ch0/ch0-01.html">
<i class="fa fa-check"></i>
<b>0.1.</b>
Go語言起源
</a>
</li>
<li class="chapter " data-level="0.2" data-path="ch0/ch0-02.html">
<a href="../ch0/ch0-02.html">
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<b>0.2.</b>
Go語言項目
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<li class="chapter " data-level="0.3" data-path="ch0/ch0-03.html">
<a href="../ch0/ch0-03.html">
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<b>0.3.</b>
本書的組織
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<li class="chapter " data-level="0.4" data-path="ch0/ch0-04.html">
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<b>0.4.</b>
更多的信息
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<li class="chapter " data-level="0.5" data-path="ch0/ch0-05.html">
<a href="../ch0/ch0-05.html">
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<b>0.5.</b>
緻謝
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="1" data-path="ch1/ch1.html">
<a href="../ch1/ch1.html">
<i class="fa fa-check"></i>
<b>1.</b>
入門
</a>
<ul class="articles">
<li class="chapter " data-level="1.1" data-path="ch1/ch1-01.html">
<a href="../ch1/ch1-01.html">
<i class="fa fa-check"></i>
<b>1.1.</b>
Hello, World
</a>
</li>
<li class="chapter " data-level="1.2" data-path="ch1/ch1-02.html">
<a href="../ch1/ch1-02.html">
<i class="fa fa-check"></i>
<b>1.2.</b>
命令行參數
</a>
</li>
<li class="chapter " data-level="1.3" data-path="ch1/ch1-03.html">
<a href="../ch1/ch1-03.html">
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<b>1.3.</b>
査找重復的行
</a>
</li>
<li class="chapter " data-level="1.4" data-path="ch1/ch1-04.html">
<a href="../ch1/ch1-04.html">
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<b>1.4.</b>
GIF動畫
</a>
</li>
<li class="chapter " data-level="1.5" data-path="ch1/ch1-05.html">
<a href="../ch1/ch1-05.html">
<i class="fa fa-check"></i>
<b>1.5.</b>
穫取URL
</a>
</li>
<li class="chapter " data-level="1.6" data-path="ch1/ch1-06.html">
<a href="../ch1/ch1-06.html">
<i class="fa fa-check"></i>
<b>1.6.</b>
併髮穫取多個URL
</a>
</li>
<li class="chapter " data-level="1.7" data-path="ch1/ch1-07.html">
<a href="../ch1/ch1-07.html">
<i class="fa fa-check"></i>
<b>1.7.</b>
Web服務
</a>
</li>
<li class="chapter " data-level="1.8" data-path="ch1/ch1-08.html">
<a href="../ch1/ch1-08.html">
<i class="fa fa-check"></i>
<b>1.8.</b>
本章要點
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="2" data-path="ch2/ch2.html">
<a href="../ch2/ch2.html">
<i class="fa fa-check"></i>
<b>2.</b>
程序結構
</a>
<ul class="articles">
<li class="chapter " data-level="2.1" data-path="ch2/ch2-01.html">
<a href="../ch2/ch2-01.html">
<i class="fa fa-check"></i>
<b>2.1.</b>
命名
</a>
</li>
<li class="chapter " data-level="2.2" data-path="ch2/ch2-02.html">
<a href="../ch2/ch2-02.html">
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<b>2.2.</b>
聲明
</a>
</li>
<li class="chapter " data-level="2.3" data-path="ch2/ch2-03.html">
<a href="../ch2/ch2-03.html">
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<b>2.3.</b>
變量
</a>
</li>
<li class="chapter " data-level="2.4" data-path="ch2/ch2-04.html">
<a href="../ch2/ch2-04.html">
<i class="fa fa-check"></i>
<b>2.4.</b>
賦值
</a>
</li>
<li class="chapter " data-level="2.5" data-path="ch2/ch2-05.html">
<a href="../ch2/ch2-05.html">
<i class="fa fa-check"></i>
<b>2.5.</b>
類型
</a>
</li>
<li class="chapter " data-level="2.6" data-path="ch2/ch2-06.html">
<a href="../ch2/ch2-06.html">
<i class="fa fa-check"></i>
<b>2.6.</b>
包和文件
</a>
</li>
<li class="chapter active" data-level="2.7" data-path="ch2/ch2-07.html">
<a href="../ch2/ch2-07.html">
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<b>2.7.</b>
作用域
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="3" data-path="ch3/ch3.html">
<a href="../ch3/ch3.html">
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<b>3.</b>
基礎數據類型
</a>
<ul class="articles">
<li class="chapter " data-level="3.1" data-path="ch3/ch3-01.html">
<a href="../ch3/ch3-01.html">
<i class="fa fa-check"></i>
<b>3.1.</b>
整型
</a>
</li>
<li class="chapter " data-level="3.2" data-path="ch3/ch3-02.html">
<a href="../ch3/ch3-02.html">
<i class="fa fa-check"></i>
<b>3.2.</b>
浮點數
</a>
</li>
<li class="chapter " data-level="3.3" data-path="ch3/ch3-03.html">
<a href="../ch3/ch3-03.html">
<i class="fa fa-check"></i>
<b>3.3.</b>
復數
</a>
</li>
<li class="chapter " data-level="3.4" data-path="ch3/ch3-04.html">
<a href="../ch3/ch3-04.html">
<i class="fa fa-check"></i>
<b>3.4.</b>
佈爾型
</a>
</li>
<li class="chapter " data-level="3.5" data-path="ch3/ch3-05.html">
<a href="../ch3/ch3-05.html">
<i class="fa fa-check"></i>
<b>3.5.</b>
字符串
</a>
</li>
<li class="chapter " data-level="3.6" data-path="ch3/ch3-06.html">
<a href="../ch3/ch3-06.html">
<i class="fa fa-check"></i>
<b>3.6.</b>
常量
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="4" data-path="ch4/ch4.html">
<a href="../ch4/ch4.html">
<i class="fa fa-check"></i>
<b>4.</b>
復閤數據類型
</a>
<ul class="articles">
<li class="chapter " data-level="4.1" data-path="ch4/ch4-01.html">
<a href="../ch4/ch4-01.html">
<i class="fa fa-check"></i>
<b>4.1.</b>
數組
</a>
</li>
<li class="chapter " data-level="4.2" data-path="ch4/ch4-02.html">
<a href="../ch4/ch4-02.html">
<i class="fa fa-check"></i>
<b>4.2.</b>
切片
</a>
</li>
<li class="chapter " data-level="4.3" data-path="ch4/ch4-03.html">
<a href="../ch4/ch4-03.html">
<i class="fa fa-check"></i>
<b>4.3.</b>
字典
</a>
</li>
<li class="chapter " data-level="4.4" data-path="ch4/ch4-04.html">
<a href="../ch4/ch4-04.html">
<i class="fa fa-check"></i>
<b>4.4.</b>
結構體
</a>
</li>
<li class="chapter " data-level="4.5" data-path="ch4/ch4-05.html">
<a href="../ch4/ch4-05.html">
<i class="fa fa-check"></i>
<b>4.5.</b>
JSON
</a>
</li>
<li class="chapter " data-level="4.6" data-path="ch4/ch4-06.html">
<a href="../ch4/ch4-06.html">
<i class="fa fa-check"></i>
<b>4.6.</b>
文本和HTML模闆
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="5" data-path="ch5/ch5.html">
<a href="../ch5/ch5.html">
<i class="fa fa-check"></i>
<b>5.</b>
函數
</a>
<ul class="articles">
<li class="chapter " data-level="5.1" data-path="ch5/ch5-01.html">
<a href="../ch5/ch5-01.html">
<i class="fa fa-check"></i>
<b>5.1.</b>
函數聲明
</a>
</li>
<li class="chapter " data-level="5.2" data-path="ch5/ch5-02.html">
<a href="../ch5/ch5-02.html">
<i class="fa fa-check"></i>
<b>5.2.</b>
遞歸
</a>
</li>
<li class="chapter " data-level="5.3" data-path="ch5/ch5-03.html">
<a href="../ch5/ch5-03.html">
<i class="fa fa-check"></i>
<b>5.3.</b>
多返迴值
</a>
</li>
<li class="chapter " data-level="5.4" data-path="ch5/ch5-04.html">
<a href="../ch5/ch5-04.html">
<i class="fa fa-check"></i>
<b>5.4.</b>
錯誤
</a>
</li>
<li class="chapter " data-level="5.5" data-path="ch5/ch5-05.html">
<a href="../ch5/ch5-05.html">
<i class="fa fa-check"></i>
<b>5.5.</b>
函數值
</a>
</li>
<li class="chapter " data-level="5.6" data-path="ch5/ch5-06.html">
<a href="../ch5/ch5-06.html">
<i class="fa fa-check"></i>
<b>5.6.</b>
匿名函數
</a>
</li>
<li class="chapter " data-level="5.7" data-path="ch5/ch5-07.html">
<a href="../ch5/ch5-07.html">
<i class="fa fa-check"></i>
<b>5.7.</b>
可變參數
</a>
</li>
<li class="chapter " data-level="5.8" data-path="ch5/ch5-08.html">
<a href="../ch5/ch5-08.html">
<i class="fa fa-check"></i>
<b>5.8.</b>
Deferred函數
</a>
</li>
<li class="chapter " data-level="5.9" data-path="ch5/ch5-09.html">
<a href="../ch5/ch5-09.html">
<i class="fa fa-check"></i>
<b>5.9.</b>
Panic異常
</a>
</li>
<li class="chapter " data-level="5.10" data-path="ch5/ch5-10.html">
<a href="../ch5/ch5-10.html">
<i class="fa fa-check"></i>
<b>5.10.</b>
Recover捕穫異常
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="6" data-path="ch6/ch6.html">
<a href="../ch6/ch6.html">
<i class="fa fa-check"></i>
<b>6.</b>
方法
</a>
<ul class="articles">
<li class="chapter " data-level="6.1" data-path="ch6/ch6-01.html">
<a href="../ch6/ch6-01.html">
<i class="fa fa-check"></i>
<b>6.1.</b>
方法聲明
</a>
</li>
<li class="chapter " data-level="6.2" data-path="ch6/ch6-02.html">
<a href="../ch6/ch6-02.html">
<i class="fa fa-check"></i>
<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">
<i class="fa fa-check"></i>
<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">
<i class="fa fa-check"></i>
<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">
<i class="fa fa-check"></i>
<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">
<i class="fa fa-check"></i>
<b>6.6.</b>
封裝
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="7" data-path="ch7/ch7.html">
<a href="../ch7/ch7.html">
<i class="fa fa-check"></i>
<b>7.</b>
接口
</a>
<ul class="articles">
<li class="chapter " 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
</a>
</li>
<li class="chapter " data-level="7.3" data-path="ch7/ch7-03.html">
<a href="../ch7/ch7-03.html">
<i class="fa fa-check"></i>
<b>7.3.</b>
實現接口的條件
</a>
</li>
<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
</a>
</li>
<li class="chapter " data-level="7.5" data-path="ch7/ch7-05.html">
<a href="../ch7/ch7-05.html">
<i class="fa fa-check"></i>
<b>7.5.</b>
接口值
</a>
</li>
<li class="chapter " data-level="7.6" data-path="ch7/ch7-06.html">
<a href="../ch7/ch7-06.html">
<i class="fa fa-check"></i>
<b>7.6.</b>
sort.Interface接口
</a>
</li>
<li class="chapter " data-level="7.7" data-path="ch7/ch7-07.html">
<a href="../ch7/ch7-07.html">
<i class="fa fa-check"></i>
<b>7.7.</b>
http.Handler接口
</a>
</li>
<li class="chapter " data-level="7.8" data-path="ch7/ch7-08.html">
<a href="../ch7/ch7-08.html">
<i class="fa fa-check"></i>
<b>7.8.</b>
error接口
</a>
</li>
<li class="chapter " data-level="7.9" data-path="ch7/ch7-09.html">
<a href="../ch7/ch7-09.html">
<i class="fa fa-check"></i>
<b>7.9.</b>
示例: 錶達式求值
</a>
</li>
<li class="chapter " data-level="7.10" data-path="ch7/ch7-10.html">
<a href="../ch7/ch7-10.html">
<i class="fa fa-check"></i>
<b>7.10.</b>
類型斷言
</a>
</li>
<li class="chapter " data-level="7.11" data-path="ch7/ch7-11.html">
<a href="../ch7/ch7-11.html">
<i class="fa fa-check"></i>
<b>7.11.</b>
基於類型斷言識彆錯誤類型
</a>
</li>
<li class="chapter " data-level="7.12" data-path="ch7/ch7-12.html">
<a href="../ch7/ch7-12.html">
<i class="fa fa-check"></i>
<b>7.12.</b>
通過類型斷言査詢接口
</a>
</li>
<li class="chapter " data-level="7.13" data-path="ch7/ch7-13.html">
<a href="../ch7/ch7-13.html">
<i class="fa fa-check"></i>
<b>7.13.</b>
類型分支
</a>
</li>
<li class="chapter " data-level="7.14" data-path="ch7/ch7-14.html">
<a href="../ch7/ch7-14.html">
<i class="fa fa-check"></i>
<b>7.14.</b>
示例: 基於標記的XML解碼
</a>
</li>
<li class="chapter " data-level="7.15" data-path="ch7/ch7-15.html">
<a href="../ch7/ch7-15.html">
<i class="fa fa-check"></i>
<b>7.15.</b>
補充幾點
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="8" data-path="ch8/ch8.html">
<a href="../ch8/ch8.html">
<i class="fa fa-check"></i>
<b>8.</b>
Goroutines和Channels
</a>
<ul class="articles">
<li class="chapter " data-level="8.1" data-path="ch8/ch8-01.html">
<a href="../ch8/ch8-01.html">
<i class="fa fa-check"></i>
<b>8.1.</b>
Goroutines
</a>
</li>
<li class="chapter " data-level="8.2" data-path="ch8/ch8-02.html">
<a href="../ch8/ch8-02.html">
<i class="fa fa-check"></i>
<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>
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<a href="../" >Go编程语言</a>
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<section class="normal" id="section-">
<h2 id="27-&#x4F5C;&#x7528;&#x57DF;">2.7. &#x4F5C;&#x7528;&#x57DF;</h2>
<p>&#x4E00;&#x500B;&#x8072;&#x660E;&#x8A9E;&#x53E5;&#x5C07;&#x7A0B;&#x5E8F;&#x4E2D;&#x7684;&#x5BE6;&#x9AD4;&#x548C;&#x4E00;&#x500B;&#x540D;&#x5B57;&#x95DC;&#x806F;, &#x6BD4;&#x5982;&#x4E00;&#x500B;&#x51FD;&#x6578;&#x6216;&#x4E00;&#x500B;&#x8B8A;&#x91CF;. &#x8072;&#x660E;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x662F;&#x6307;&#x6E90;&#x4EE3;&#x78BC;&#x4E2D;&#x53EF;&#x4EE5;&#x6709;&#x6548;&#x4F7F;&#x7528;&#x9019;&#x500B;&#x540D;&#x5B57;&#x7684;&#x7BC4;&#x570D;.</p>
<p>&#x4E0D;&#x8981;&#x5C07;&#x4F5C;&#x7528;&#x57DF;&#x548C;&#x751F;&#x547D;&#x9031;&#x671F;&#x6DF7;&#x70BA;&#x4E00;&#x8AC7;. &#x8072;&#x660E;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x5C0D;&#x61C9;&#x7684;&#x662F;&#x4E00;&#x500B;&#x6E90;&#x4EE3;&#x78BC;&#x7684;&#x6587;&#x672C;&#x5340;&#x57DF;; &#x5B83;&#x662F;&#x4E00;&#x500B;&#x7DE8;&#x8B6F;&#x6642;&#x7684;&#x5C6C;&#x6027;. &#x4E00;&#x500B;&#x8B8A;&#x91CF;&#x7684;&#x751F;&#x547D;&#x9031;&#x671F;&#x662F;&#x7A0B;&#x5E8F;&#x904B;&#x884C;&#x6642;&#x8B8A;&#x91CF;&#x5B58;&#x5728;&#x7684;&#x6709;&#x6548;&#x6642;&#x9593;&#x6BB5;, &#x5728;&#x6B64;&#x6642;&#x9593;&#x5340;&#x57DF;&#x5167;&#x5B58;&#x5B83;&#x53EF;&#x4EE5;&#x88AB;&#x7A0B;&#x5E8F;&#x7684;&#x5176;&#x4ED6;&#x90E8;&#x5206;&#x5F15;&#x7528;. &#x662F;&#x4E00;&#x500B;&#x904B;&#x884C;&#x6642;&#x7684;&#x6982;&#x5538;.</p>
<p>&#x8A9E;&#x6CD5;&#x584A;&#x662F;&#x7531;&#x82B1;&#x62EC;&#x5F27;&#x6240;&#x5305;&#x542B;&#x7684;&#x4E00;&#x7E6B;&#x5217;&#x8A9E;&#x53E5;, &#x5C31;&#x50CF;&#x51FD;&#x6578;&#x9AD4;&#x6216;&#x5FAA;&#x74B0;&#x9AD4;&#x90A3;&#x6A23;. &#x8A9E;&#x6CD5;&#x584A;&#x5167;&#x90E8;&#x8072;&#x660E;&#x7684;&#x540D;&#x5B57;&#x662F;&#x7121;&#x6CD5;&#x88AB;&#x5916;&#x90E8;&#x8A9E;&#x6CD5;&#x584A;&#x8A2A;&#x554F;&#x7684;. &#x8A9E;&#x6CD5;&#x6C7A;&#x5B9A;&#x4E86;&#x5167;&#x90E8;&#x8072;&#x660E;&#x7684;&#x540D;&#x5B57;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x7BC4;&#x570D;. &#x6211;&#x5011;&#x53EF;&#x4EE5;&#x9019;&#x6A23;&#x7406;&#x89E3;, &#x8A9E;&#x6CD5;&#x584A;&#x53EF;&#x4EE5;&#x5305;&#x542B;&#x5176;&#x4ED6;&#x985E;&#x4F3C;&#x7D44;&#x6279;&#x91CF;&#x8072;&#x660E;&#x7B49;&#x6C92;&#x6709;&#x7528;&#x82B1;&#x62EC;&#x5F27;&#x5305;&#x542B;&#x7684;&#x4EE3;&#x78BC;, &#x6211;&#x5011;&#x7A31;&#x4E4B;&#x70BA;&#x8A5E;&#x6ED9;&#x584A;. &#x6709;&#x4E00;&#x500B;&#x8A9E;&#x6CD5;&#x6C7A;&#x70BA;&#x6574;&#x500B;&#x6E90;&#x4EE3;&#x78BC;, &#x7A31;&#x70BA;&#x5168;&#x4FB7;&#x584A;; &#x7136;&#x5F8C;&#x662F;&#x6BCF;&#x500B;&#x5305;&#x7684;&#x8A9E;&#x6CD5;&#x6C7A;; &#x6BCF;&#x500B; for, if &#x548C; switch &#x8A9E;&#x53E5;&#x7684;&#x8A9E;&#x6CD5;&#x6C7A;; &#x6BCF;&#x500B; switch &#x6216; select &#x5206;&#x652F;&#x7684; &#x8A9E;&#x6CD5;&#x6C7A;; &#x7576;&#x7136;&#x4E5F;&#x5305;&#x542B;&#x986F;&#x793A;&#x7DE8;&#x5BEB;&#x7684;&#x8A9E;&#x6CD5;&#x584A;(&#x82B1;&#x62EC;&#x5F27;&#x5305;&#x542B;).</p>
<p>&#x8072;&#x660E;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x6C7A;&#x5B9A;&#x4E86;&#x4F5C;&#x7528;&#x57DF;&#x7BC4;&#x570D;&#x662F;&#x5927;&#x9084;&#x662F;&#x5C0F;. &#x5167;&#x7F6E;&#x7684;&#x985E;&#x578B;, &#x51FD;&#x6578;&#x548C;&#x5E38;&#x91CF;, &#x6BD4;&#x5982; int, len &#x548C; true &#x7B49;&#x662F;&#x5728;&#x5168;&#x4FB7;&#x4F5C;&#x7528;&#x57DF;&#x7684;, &#x53EF;&#x4EE5;&#x5728;&#x6574;&#x500B;&#x7A0B;&#x5E8F;&#x4E2D;&#x76F4;&#x63A5;&#x4F7F;&#x7528;. &#x4EFB;&#x4F55;&#x5728;&#x5728;&#x51FD;&#x6578;&#x5916;&#x90E8;(&#x4E5F;&#x5C31;&#x662F;&#x5305;&#x7D1A;&#x4F5C;&#x7528;&#x57DF;)&#x8072;&#x660E;&#x7684;&#x540D;&#x5B57;&#x53EF;&#x4EE5;&#x5728;&#x8855;&#x4E00;&#x500B;&#x5305;&#x7684;&#x4EFB;&#x4F55;Go&#x6587;&#x4EF6;&#x8A2A;&#x554F;. &#x5C0E;&#x5165;&#x7684;&#x5305;, &#x4F8B;&#x5982; tempconv &#x5C0E;&#x5165;&#x7684; fmt &#x5305;, &#x5247;&#x662F;&#x5C0D;&#x61C9;&#x6587;&#x4EF6;&#x7D1A;&#x7684;&#x4F5C;&#x7528;&#x57DF;, &#x56E0;&#x6B64;&#x96BB;&#x80FD;&#x5728;&#x7576;&#x524D;&#x7684;&#x6587;&#x4EF6;&#x4E2D;&#x8A2A;&#x554F; fmt &#x5305;, &#x7576;&#x524D;&#x5305;&#x7684;&#x5176;&#x5B83;&#x6587;&#x4EF6;&#x7121;&#x6CD5;&#x8A2A;&#x554F;&#x7576;&#x524D;&#x6587;&#x4EF6;&#x5C0E;&#x5165;&#x7684;&#x5305;. &#x9084;&#x6709;&#x8A31;&#x591A;&#x8072;&#x660E;, &#x6BD4;&#x5982; tempconv.CToF &#x51FD;&#x6578;&#x4E2D;&#x7684;&#x8B8A;&#x91CF; c, &#x5247;&#x662F;&#x4FB7;&#x90E8;&#x4F5C;&#x7528;&#x57DF;&#x7684;, &#x5B83;&#x96BB;&#x80FD;&#x5728;&#x51FD;&#x6578;&#x5167;&#x90E8;(&#x751A;&#x81F3;&#x96BB;&#x80FD;&#x662F;&#x67D0;&#x4E9B;&#x90E8;&#x5206;)&#x8A2A;&#x554F;.</p>
<p>&#x63A7;&#x88FD;&#x6D41;&#x6A19;&#x7C3D;, &#x4F8B;&#x5982; break, continue &#x6216; goto &#x5F8C;&#x9EAB;&#x8DDF;&#x7740;&#x7684;&#x90A3;&#x7A2E;&#x6A19;&#x7C3D;, &#x5247;&#x662F;&#x51FD;&#x6578;&#x7D1A;&#x7684;&#x4F5C;&#x7528;&#x57DF;.</p>
<p>&#x4E00;&#x500B;&#x7A0B;&#x5E8F;&#x53EF;&#x80FD;&#x5305;&#x542B;&#x591A;&#x500B;&#x8855;&#x540D;&#x7684;&#x8072;&#x660E;, &#x96BB;&#x6709;&#x5B83;&#x5011;&#x5728;&#x4E0D;&#x8855;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x5C31;&#x6C92;&#x6709;&#x95DC;&#x7E6B;. &#x4F8B;&#x5982;, &#x4F60;&#x53EF;&#x4EE5;&#x8072;&#x660E;&#x4E00;&#x500B;&#x4FB7;&#x90E8;&#x8B8A;&#x91CF;, &#x548C;&#x5305;&#x7D1A;&#x7684;&#x8B8A;&#x91CF;&#x8855;&#x540D;. &#x6216;&#x8005;&#x662F; 2.3.3&#x7BC0;&#x7684;&#x90A3;&#x6A23;, &#x4F60;&#x53EF;&#x4EE5;&#x5C07;&#x4E00;&#x500B;&#x51FD;&#x6578;&#x53C3;&#x6578;&#x7684;&#x540D;&#x5B57;&#x8072;&#x660E;&#x70BA; new, &#x96D6;&#x7136;&#x5167;&#x7F6E;&#x7684;new&#x662F;&#x5168;&#x4FB7;&#x4F5C;&#x7528;&#x57DF;&#x7684;. &#x4F46;&#x662F;&#x7269;&#x6975;&#x5FC5;&#x53CD;, &#x5982;&#x679C;&#x6FEB;&#x7528;&#x91CD;&#x540D;&#x7684;&#x7279;&#x6027;, &#x53EF;&#x80FD;&#x5C0E;&#x7DFB;&#x7A0B;&#x5E8F;&#x5F88;&#x96E3;&#x95B1;&#x8B80;.</p>
<p>&#x7576;&#x7DE8;&#x8B6F;&#x5668;&#x9047;&#x5230;&#x4E00;&#x500B;&#x540D;&#x5B57;&#x5F15;&#x7528;, &#x5B83;&#x770B;&#x8D77;&#x4F86;&#x50CF;&#x4E00;&#x500B;&#x8072;&#x660E;, &#x5B83;&#x9996;&#x5148;&#x5F9E;&#x6700;&#x5167;&#x5C64;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x66CF;&#x5168;&#x4FB7;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x67FB;&#x627E;. &#x5982;&#x679C;&#x67FB;&#x627E;&#x5931;&#x6557;, &#x5247;&#x5831;&#x544A; &quot;&#x672A;&#x8072;&#x660E;&#x7684;&#x540D;&#x5B57;&quot; &#x9019;&#x6A23;&#x7684;&#x932F;&#x8AA4;. &#x5982;&#x679C;&#x540D;&#x5B57;&#x5728;&#x5167;&#x90E8;&#x548C;&#x5916;&#x90E8;&#x7684;&#x584A;&#x5206;&#x5F46;&#x8072;&#x660E;, &#x5247;&#x5167;&#x90E8;&#x584A;&#x7684;&#x8072;&#x660E;&#x9996;&#x5148;&#x88AB;&#x627E;&#x5230;. &#x5728;&#x9019;&#x7A2E;&#x60C5;&#x6CC1;&#x4E0B;, &#x5167;&#x90E8;&#x8072;&#x660E;&#x5C4F;&#x853D;&#x4E86;&#x5916;&#x90E8;&#x8855;&#x540D;&#x7684;&#x8072;&#x660E;, &#x8B93;&#x5916;&#x90E8;&#x7684;&#x8072;&#x660E;&#x7121;&#x6CD5;&#x88AB;&#x8A2A;&#x554F;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> f() {}
<span class="hljs-keyword">var</span> g = <span class="hljs-string">&quot;g&quot;</span>
<span class="hljs-keyword">func</span> main() {
f := <span class="hljs-string">&quot;f&quot;</span>
fmt.Println(f) <span class="hljs-comment">// &quot;f&quot;; local var f shadows package-level func f</span>
fmt.Println(g) <span class="hljs-comment">// &quot;g&quot;; package-level var</span>
fmt.Println(h) <span class="hljs-comment">// compile error: undefined: h</span>
}
</code></pre>
<p>&#x5728;&#x51FD;&#x6578;&#x4E2D;&#x8A5E;&#x6CD5;&#x57DF;&#x53EF;&#x4EE5;&#x6DF1;&#x5EA6;&#x5D4C;&#x5957;, &#x56E0;&#x6B64;&#x5167;&#x90E8;&#x7684;&#x4E00;&#x500B;&#x8072;&#x660E;&#x53EF;&#x80FD;&#x5C4F;&#x853D;&#x5916;&#x90E8;&#x7684;&#x8072;&#x660E;. &#x9084;&#x6709;&#x8A31;&#x591A;&#x584A;&#x662F;if&#x6216;for&#x7B49;&#x63A7;&#x88FD;&#x6D41;&#x8A9E;&#x53E5;&#x69CB;&#x9020;&#x7684;. &#x4E0B;&#x9EAB;&#x7684;&#x4EE3;&#x78BC;&#x6709;&#x4E09;&#x500B;&#x4E0D;&#x8855;&#x7684;&#x8B8A;&#x91CF;x, &#x56E0;&#x70BA;&#x5B83;&#x5011;&#x662F;&#x5B9A;&#x7FA9;&#x5728;&#x4E0D;&#x8855;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x7684;&#x539F;&#x56E0;. (&#x9019;&#x500B;&#x4F8B;&#x5B50;&#x96BB;&#x662F;&#x70BA;&#x4E86;&#x6F14;&#x793A;&#x4F5C;&#x7528;&#x57DF;&#x898F;&#x5247;, &#x4F46;&#x4E0D;&#x662F;&#x597D;&#x7684;&#x7DE8;&#x7A0B;&#x98A8;&#x683C;.)</p>
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> main() {
x := <span class="hljs-string">&quot;hello!&quot;</span>
<span class="hljs-keyword">for</span> i := <span class="hljs-number">0</span>; i &lt; <span class="hljs-built_in">len</span>(x); i++ {
x := x[i]
<span class="hljs-keyword">if</span> x != <span class="hljs-string">&apos;!&apos;</span> {
x := x + <span class="hljs-string">&apos;A&apos;</span> - <span class="hljs-string">&apos;a&apos;</span>
fmt.Printf(<span class="hljs-string">&quot;%c&quot;</span>, x) <span class="hljs-comment">// &quot;HELLO&quot; (one letter per iteration)</span>
}
}
}
</code></pre>
<p>&#x5728; <code>x[i]</code> &#x548C; <code>x + &apos;A&apos; - &apos;a&apos;</code> &#x8072;&#x660E;&#x521D;&#x59CB;&#x5316;&#x7684;&#x9336;&#x9054;&#x5F0F;&#x4E2D;&#x90FD;&#x5F15;&#x7528;&#x4E86;&#x5916;&#x90E8;&#x4F5C;&#x7528;&#x57DF;&#x8072;&#x660E;&#x7684;x&#x8B8A;&#x91CF;, &#x7A0D;&#x5F8C;&#x6211;&#x5011;&#x6703;&#x89E3;&#x91CB;&#x9019;&#x500B;. (&#x8A3B;&#x610F;, &#x5F8C;&#x9EAB;&#x7684;&#x9336;&#x9054;&#x5F0F;&#x548C;unicode.ToUpper&#x4F75;&#x4E0D;&#x7B49;&#x50F9;.)</p>
<p>&#x6B63;&#x5982;&#x4E0A;&#x9EAB;&#x6240;&#x793A;, &#x4F75;&#x4E0D;&#x662F;&#x6240;&#x6709;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x90FD;&#x986F;&#x793A;&#x5730;&#x5C0D;&#x61C9;&#x5230;&#x7531;&#x82B1;&#x62EC;&#x5F27;&#x5305;&#x542B;&#x7684;&#x8A9E;&#x53E5;; &#x9084;&#x6709;&#x4E00;&#x4E9B;&#x96B1;&#x542B;&#x7684;&#x898F;&#x5247;. &#x4E0A;&#x9EAB;&#x7684;for&#x8A9E;&#x53E5;&#x5275;&#x5EFA;&#x4E86;&#x5169;&#x500B;&#x8A5E;&#x6CD5;&#x57DF;: &#x82B1;&#x62EC;&#x5F27;&#x5305;&#x542B;&#x7684;&#x662F;&#x986F;&#x5F0F;&#x7684;&#x90E8;&#x5206;&#x662F;for&#x7684;&#x5FAA;&#x74B0;&#x9AD4;, &#x53E6;&#x5916;&#x4E00;&#x500B;&#x96B1;&#x5F0F;&#x7684;&#x90E8;&#x5206;&#x5247;&#x662F;&#x5FAA;&#x74B0;&#x7684;&#x521D;&#x59CB;&#x5316;&#x90E8;&#x5206;, &#x6BD4;&#x5982;&#x7528;&#x65BC;&#x8FED;&#x4EE3;&#x8B8A;&#x91CF; i &#x7684;&#x521D;&#x59CB;&#x5316;. &#x96B1;&#x5F0F;&#x7684;&#x90E8;&#x5206;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x9084;&#x5305;&#x542B;&#x689D;&#x4EF6;&#x6E2C;&#x8A66;&#x90E8;&#x5206;&#x548C;&#x5FAA;&#x74B0;&#x5F8C;&#x7684;&#x8FED;&#x4EE3;&#x90E8;&#x5206;(i++), &#x7576;&#x7136;&#x4E5F;&#x5305;&#x542B;&#x5FAA;&#x74B0;&#x9AD4;.</p>
<p>&#x4E0B;&#x9EAB;&#x7684;&#x4F8B;&#x5B50;&#x8855;&#x6A23;&#x6709;&#x4E09;&#x500B;&#x4E0D;&#x8855;&#x7684;x&#x8B8A;&#x91CF;, &#x6BCF;&#x500B;&#x8072;&#x660E;&#x5728;&#x4E0D;&#x8855;&#x7684;&#x584A;, &#x4E00;&#x500B;&#x5728;&#x51FD;&#x6578;&#x9AD4;&#x584A;, &#x4E00;&#x500B;&#x5728;for&#x8A9E;&#x53E5;&#x584A;, &#x4E00;&#x500B;&#x5728;&#x5FAA;&#x74B0;&#x9AD4;&#x584A;; &#x96BB;&#x6709;&#x5169;&#x500B;&#x584A;&#x662F;&#x986F;&#x5F0F;&#x5275;&#x5EFA;&#x7684;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> main() {
x := <span class="hljs-string">&quot;hello&quot;</span>
<span class="hljs-keyword">for</span> _, x := <span class="hljs-keyword">range</span> x {
x := x + <span class="hljs-string">&apos;A&apos;</span> - <span class="hljs-string">&apos;a&apos;</span>
fmt.Printf(<span class="hljs-string">&quot;%c&quot;</span>, x) <span class="hljs-comment">// &quot;HELLO&quot; (one letter per iteration)</span>
}
}
</code></pre>
<p>&#x548C;&#x5F7F;&#x5982;&#x5FAA;&#x74B0;&#x985E;&#x4F3C;, if&#x548C;switch&#x8A9E;&#x53E5;&#x4E5F;&#x6703;&#x5728;&#x689D;&#x4EF6;&#x90E8;&#x5206;&#x5275;&#x5EFA;&#x96B1;&#x5F0F;&#x584A;, &#x9084;&#x6709;&#x5B83;&#x5011;&#x5C0D;&#x61C9;&#x7684;&#x57F7;&#x884C;&#x9AD4;&#x584A;. &#x4E0B;&#x9EAB;&#x7684; if-else &#x6E2C;&#x8A66;&#x93C8;&#x6F14;&#x793A;&#x7684; x &#x548C; y &#x7684;&#x4F5C;&#x7528;&#x57DF;&#x7BC4;&#x570D;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">if</span> x := f(); x == <span class="hljs-number">0</span> {
fmt.Println(x)
} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> y := g(x); x == y {
fmt.Println(x, y)
} <span class="hljs-keyword">else</span> {
fmt.Println(x, y)
}
fmt.Println(x, y) <span class="hljs-comment">// compile error: x and y are not visible here</span>
</code></pre>
<p>&#x7B2C;&#x4E8C;&#x500B;if&#x8A9E;&#x53E5;&#x5D4C;&#x5957;&#x5728;&#x7B2C;&#x4E00;&#x500B;&#x5167;&#x90E8;, &#x56E0;&#x6B64;&#x4E00;&#x500B;if&#x8A9E;&#x53E5;&#x689D;&#x4EF6;&#x584A;&#x8072;&#x660E;&#x7684;&#x8B8A;&#x91CF;&#x5728;&#x7B2C;&#x4E8C;&#x500B;if&#x4E2D;&#x4E5F;&#x53EF;&#x4EE5;&#x8A2A;&#x554F;. switch&#x8A9E;&#x53E5;&#x7684;&#x6BCF;&#x500B;&#x5206;&#x652F;&#x4E5F;&#x6709;&#x985E;&#x4F3C;&#x7684;&#x898F;&#x5247;: &#x689D;&#x4EF6;&#x90E8;&#x5206;&#x70BA;&#x4E00;&#x500B;&#x96B1;&#x5F0F;&#x584A;, &#x7136;&#x5F8C;&#x6BCF;&#x500B;&#x662F;&#x6BCF;&#x500B;&#x5206;&#x652F;&#x7684;&#x4E3B;&#x9AD4;&#x584A;.</p>
<p>&#x5728;&#x5305;&#x7D1A;&#x5F46;, &#x8072;&#x660E;&#x7684;&#x9806;&#x5E8F;&#x4F75;&#x4E0D;&#x6703;&#x5F71;&#x97FF;&#x4F5C;&#x7528;&#x57DF;&#x7BC4;&#x570D;, &#x56E0;&#x6B64;&#x4E00;&#x500B;&#x5148;&#x8072;&#x660E;&#x7684;&#x53EF;&#x4EE5;&#x5F15;&#x7528;&#x5B83;&#x81EA;&#x8EAB;&#x6216;&#x8005;&#x662F;&#x5F15;&#x7528;&#x5F8C;&#x9EAB;&#x7684;&#x4E00;&#x500B;&#x8072;&#x660E;, &#x9019;&#x53EF;&#x4EE5;&#x8B93;&#x6211;&#x5011;&#x5B9A;&#x7FA9;&#x4E00;&#x4E9B;&#x76F8;&#x4E92;&#x5D4C;&#x5957;&#x6216;&#x905E;&#x6B78;&#x7684;&#x985E;&#x578B;&#x6216;&#x51FD;&#x6578;. &#x4F46;&#x662F;&#x5982;&#x679C;&#x4E00;&#x500B;&#x8B8A;&#x91CF;&#x6216;&#x5E38;&#x91CF;&#x905E;&#x6B78;&#x5F15;&#x7528;&#x4E86;&#x81EA;&#x8EAB;, &#x5247;&#x6703;&#x7522;&#x751F;&#x7DE8;&#x8B6F;&#x932F;&#x8AA4;.</p>
<p>&#x5728;&#x9019;&#x500B;&#x7A0B;&#x5E8F;&#x4E2D;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">if</span> f, err := os.Open(fname); err != <span class="hljs-constant">nil</span> { <span class="hljs-comment">// compile error: unused: f</span>
<span class="hljs-keyword">return</span> err
}
f.ReadByte() <span class="hljs-comment">// compile error: undefined f</span>
f.Close() <span class="hljs-comment">// compile error: undefined f</span>
</code></pre>
<p>&#x8B8A;&#x91CF; f &#x7684;&#x4F5C;&#x7528;&#x57DF;&#x96BB;&#x6709;if&#x8A9E;&#x53E5;&#x5167;, &#x56E0;&#x6B64;&#x5F8C;&#x9EAB;&#x7684;&#x8A9E;&#x53E5;&#x5C07;&#x7121;&#x6CD5;&#x5F15;&#x5165;&#x5B83;, &#x5C07;&#x5C0E;&#x7DFB;&#x7DE8;&#x8B6F;&#x932F;&#x8AA4;. &#x4F60;&#x53EF;&#x80FD;&#x6703;&#x6536;&#x5230;&#x4E00;&#x500B;&#x4FB7;&#x90E8;&#x8B8A;&#x91CF;f&#x6C92;&#x6709;&#x8072;&#x660E;&#x7684;&#x932F;&#x8AA4;&#x63D0;&#x793A;, &#x5177;&#x9AD4;&#x932F;&#x8AA4;&#x4FE1;&#x606F;&#x4F9D;&#x8CF4;&#x7DE8;&#x8B6F;&#x5668;&#x7684;&#x5BE6;&#x73FE;.</p>
<p>&#x901A;&#x5E38;&#x9700;&#x8981;&#x5728;if&#x4E4B;&#x524D;&#x8072;&#x660E;&#x8B8A;&#x91CF;, &#x9019;&#x6A23;&#x53EF;&#x4EE5;&#x78BA;&#x4FDD;&#x5F8C;&#x9EAB;&#x7684;&#x8A9E;&#x53E5;&#x4F9D;&#x7136;&#x53EF;&#x4EE5;&#x8A2A;&#x554F;&#x8B8A;&#x91CF;:</p>
<pre><code class="lang-Go">f, err := os.Open(fname)
<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
<span class="hljs-keyword">return</span> err
}
f.ReadByte()
f.Close()
</code></pre>
<p>&#x4F60;&#x53EF;&#x80FD;&#x6703;&#x8003;&#x616E;&#x901A;&#x904E;&#x5C07;ReadByte&#x548C;Close&#x79FB;&#x52D5;&#x5230;if&#x7684;else&#x584A;&#x4F86;&#x89E3;&#x6C7A;&#x9019;&#x500B;&#x554F;&#x984C;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">if</span> f, err := os.Open(fname); err != <span class="hljs-constant">nil</span> {
<span class="hljs-keyword">return</span> err
} <span class="hljs-keyword">else</span> {
<span class="hljs-comment">// f and err are visible here too</span>
f.ReadByte()
f.Close()
}
</code></pre>
<p>&#x4F46;&#x9019;&#x4E0D;&#x662F;Go&#x63A8;&#x85A6;&#x7684;&#x505A;&#x6CD5;, Go&#x7684;&#x7FD2;&#x6163;&#x662F;&#x5728;if&#x4E2D;&#x8655;&#x7406;&#x932F;&#x8AA4;&#x7136;&#x5F8C;&#x76F4;&#x63A5;&#x8FD4;&#x8FF4;, &#x9019;&#x6A23;&#x53EF;&#x4EE5;&#x78BA;&#x4FDD;&#x6B63;&#x5E38;&#x6210;&#x529F;&#x57F7;&#x884C;&#x7684;&#x8A9E;&#x53E5;&#x4E0D;&#x9700;&#x8981;&#x4EE3;&#x78BC;&#x7E2E;&#x9032;.</p>
<p>&#x8981;&#x7279;&#x5F46;&#x8A3B;&#x610F;&#x77ED;&#x7684;&#x8B8A;&#x91CF;&#x8072;&#x660E;&#x7684;&#x4F5C;&#x7528;&#x57DF;&#x7BC4;&#x570D;, &#x8003;&#x616E;&#x4E0B;&#x9EAB;&#x7684;&#x7A0B;&#x5E8F;, &#x5B83;&#x7684;&#x76EE;&#x7684;&#x662F;&#x7A6B;&#x53D6;&#x7576;&#x524D;&#x7684;&#x5DE5;&#x4F5C;&#x76EE;&#x5F54;&#x7136;&#x5F8C;&#x4FDD;&#x5B58;&#x5230;&#x4E00;&#x500B;&#x5305;&#x7D1A;&#x7684;&#x8B8A;&#x91CF;&#x4E2D;. &#x9019;&#x53EF;&#x4EE5;&#x901A;&#x904E;&#x76F4;&#x63A5;&#x8ABF;&#x7528; os.Getwd &#x5B8C;&#x6210;, &#x4F46;&#x662F;&#x5C07;&#x9019;&#x500B;&#x5F9E;&#x4E3B;&#x908F;&#x8F2F;&#x4E2D;&#x5206;&#x96E2;&#x9F63;&#x4F86;&#x53EF;&#x80FD;&#x6703;&#x66F4;&#x597D;, &#x7279;&#x5F46;&#x662F;&#x5728;&#x9700;&#x8981;&#x8655;&#x7406;&#x932F;&#x8AA4;&#x7684;&#x6642;&#x5019;. &#x51FD;&#x6578; log.Fatalf &#x6253;&#x5370;&#x4FE1;&#x606F;, &#x7136;&#x5F8C;&#x8ABF;&#x7528; os.Exit(1) &#x7D42;&#x6B62;&#x7A0B;&#x5E8F;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> cwd <span class="hljs-typename">string</span>
<span class="hljs-keyword">func</span> init() {
cwd, err := os.Getwd() <span class="hljs-comment">// compile error: unused: cwd</span>
<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
log.Fatalf(<span class="hljs-string">&quot;os.Getwd failed: %v&quot;</span>, err)
}
}
</code></pre>
<p>&#x96D6;&#x7136;cwd&#x5728;&#x5916;&#x90E8;&#x5DF2;&#x7D93;&#x8072;&#x660E;&#x904E;, &#x4F46;&#x662F; <code>:=</code> &#x8A9E;&#x53E5;&#x9084;&#x662F;&#x5C07; cwd &#x548C; err &#x91CD;&#x65B0;&#x8072;&#x660E;&#x70BA;&#x4FB7;&#x90E8;&#x8B8A;&#x91CF;. &#x5167;&#x90E8;&#x8072;&#x660E;&#x7684; cwd &#x5C07;&#x5C4F;&#x853D;&#x5916;&#x90E8;&#x7684;&#x8072;&#x660E;, &#x56E0;&#x6B64;&#x4E0A;&#x9EAB;&#x7684;&#x4EE3;&#x78BC;&#x4F75;&#x4E0D;&#x6703;&#x66F4;&#x65B0;&#x5305;&#x7D1A;&#x8072;&#x660E;&#x7684; cwd &#x8B8A;&#x91CF;.</p>
<p>&#x7576;&#x524D;&#x7684;&#x7DE8;&#x8B6F;&#x5668;&#x5C07;&#x6AA2;&#x6E2C;&#x5230;&#x4FB7;&#x90E8;&#x8072;&#x660E;&#x7684;cwd&#x4F75;&#x6C92;&#x6709;&#x672C;&#x4F7F;&#x7528;, &#x7136;&#x5F8C;&#x5831;&#x544A;&#x9019;&#x53EF;&#x80FD;&#x662F;&#x4E00;&#x500B;&#x932F;&#x8AA4;, &#x4F46;&#x662F;&#x9019;&#x7A2E;&#x6AA2;&#x6E2C;&#x4F75;&#x4E0D;&#x53EF;&#x9760;. &#x4E00;&#x4E9B;&#x5C0F;&#x7684;&#x4EE3;&#x78BC;&#x8B8A;&#x66F4;, &#x4F8B;&#x5982;&#x589E;&#x52A0;&#x4E00;&#x500B;&#x4FB7;&#x90E8;cwd&#x7684;&#x6253;&#x5370;&#x8A9E;&#x53E5;, &#x5C31;&#x53EF;&#x80FD;&#x5C0E;&#x7DFB;&#x9019;&#x7A2E;&#x6AA2;&#x6E2C;&#x5931;&#x6548;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> cwd <span class="hljs-typename">string</span>
<span class="hljs-keyword">func</span> init() {
cwd, err := os.Getwd() <span class="hljs-comment">// <span class="hljs-doctag">NOTE:</span> wrong!</span>
<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
log.Fatalf(<span class="hljs-string">&quot;os.Getwd failed: %v&quot;</span>, err)
}
log.Printf(<span class="hljs-string">&quot;Working directory = %s&quot;</span>, cwd)
}
</code></pre>
<p>&#x5168;&#x4FB7;&#x7684;cwd&#x8B8A;&#x91CF;&#x4F9D;&#x7136;&#x662F;&#x6C92;&#x6709;&#x88AB;&#x6B63;&#x78BA;&#x521D;&#x59CB;&#x5316;&#x7684;, &#x800C;&#x4E14;&#x770B;&#x4F3C;&#x6B63;&#x5E38;&#x7684;&#x65E5;&#x8A8C;&#x8F38;&#x9F63;&#x66F4;&#x662F;&#x9019;&#x500B;BUG&#x66F4;&#x52A0;&#x96B1;&#x6666;.</p>
<p>&#x6709;&#x8A31;&#x591A;&#x65B9;&#x5F0F;&#x53EF;&#x4EE5;&#x907F;&#x514D;&#x9F63;&#x73FE;&#x985E;&#x4F3C;&#x6F5B;&#x5728;&#x7684;&#x554F;&#x984C;. &#x6700;&#x76F4;&#x63A5;&#x7684;&#x662F;&#x901A;&#x904E;&#x55AE;&#x7368;&#x8072;&#x660E;err&#x8B8A;&#x91CF;, &#x4F86;&#x907F;&#x514D;&#x4F7F;&#x7528; <code>:=</code> &#x7684;&#x7C21;&#x77ED;&#x8072;&#x660E;&#x65B9;&#x5F0F;:</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> cwd <span class="hljs-typename">string</span>
<span class="hljs-keyword">func</span> init() {
<span class="hljs-keyword">var</span> err error
cwd, err = os.Getwd()
<span class="hljs-keyword">if</span> err != <span class="hljs-constant">nil</span> {
log.Fatalf(<span class="hljs-string">&quot;os.Getwd failed: %v&quot;</span>, err)
}
}
</code></pre>
<p>&#x6211;&#x5011;&#x5DF2;&#x7D93;&#x770B;&#x5230;&#x5305;, &#x6587;&#x4EF6;, &#x8072;&#x660E;&#x548C;&#x8A9E;&#x53E5;&#x5982;&#x4F55;&#x4F86;&#x9336;&#x9054;&#x4E00;&#x500B;&#x7A0B;&#x5E8F;&#x7D50;&#x69CB;. &#x5728;&#x4E0B;&#x9EAB;&#x7684;&#x5169;&#x500B;&#x7AE0;&#x7BC0;, &#x6211;&#x5011;&#x5C07;&#x63A2;&#x8A0E;&#x6578;&#x64DA;&#x7684;&#x7D50;&#x69CB;.</p>
<p><strong>&#x8B6F;&#x8A3B;: &#x672C;&#x7AE0;&#x7684;&#x8A5E;&#x6CD5;&#x57DF;&#x548C;&#x4F5C;&#x7528;&#x57DF;&#x6982;&#x5538;&#x6709;&#x4E9B;&#x6DF7;&#x6DC6;, &#x9700;&#x8981;&#x91CD;&#x8B6F;&#x4E00;&#x904D;.</strong></p>
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