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< ol class = "chapter" >
< li class = "chapter-item expanded " >
< a href = "../index.html" > Go语言圣经< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../preface-zh.html" > 译者序< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../preface.html" > 前言< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch4/ch4-06.html" > < strong aria-hidden = "true" > 4.6.< / strong > 文本和HTML模板< / a >
< / li >
< / ol >
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< a href = "../ch5/ch5.html" > < strong aria-hidden = "true" > 5.< / strong > 函数< / a >
< / li >
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< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-01.html" > < strong aria-hidden = "true" > 5.1.< / strong > 函数声明< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-02.html" > < strong aria-hidden = "true" > 5.2.< / strong > 递归< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-03.html" > < strong aria-hidden = "true" > 5.3.< / strong > 多返回值< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-04.html" > < strong aria-hidden = "true" > 5.4.< / strong > 错误< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-05.html" > < strong aria-hidden = "true" > 5.5.< / strong > 函数值< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-06.html" > < strong aria-hidden = "true" > 5.6.< / strong > 匿名函数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-07.html" > < strong aria-hidden = "true" > 5.7.< / strong > 可变参数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-08.html" > < strong aria-hidden = "true" > 5.8.< / strong > Deferred函数< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-09.html" > < strong aria-hidden = "true" > 5.9.< / strong > Panic异常< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5-10.html" > < strong aria-hidden = "true" > 5.10.< / strong > Recover捕获异常< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6.html" > < strong aria-hidden = "true" > 6.< / strong > 方法< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-01.html" > < strong aria-hidden = "true" > 6.1.< / strong > 方法声明< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-02.html" > < strong aria-hidden = "true" > 6.2.< / strong > 基于指针对象的方法< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-03.html" > < strong aria-hidden = "true" > 6.3.< / strong > 通过嵌入结构体来扩展类型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-04.html" > < strong aria-hidden = "true" > 6.4.< / strong > 方法值和方法表达式< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-05.html" > < strong aria-hidden = "true" > 6.5.< / strong > 示例: Bit数组< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch6/ch6-06.html" > < strong aria-hidden = "true" > 6.6.< / strong > 封装< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7.html" > < strong aria-hidden = "true" > 7.< / strong > 接口< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-01.html" > < strong aria-hidden = "true" > 7.1.< / strong > 接口是合约< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-02.html" > < strong aria-hidden = "true" > 7.2.< / strong > 接口类型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-03.html" > < strong aria-hidden = "true" > 7.3.< / strong > 实现接口的条件< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-04.html" > < strong aria-hidden = "true" > 7.4.< / strong > flag.Value接口< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-05.html" > < strong aria-hidden = "true" > 7.5.< / strong > 接口值< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-06.html" > < strong aria-hidden = "true" > 7.6.< / strong > sort.Interface接口< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-07.html" > < strong aria-hidden = "true" > 7.7.< / strong > http.Handler接口< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-08.html" > < strong aria-hidden = "true" > 7.8.< / strong > error接口< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-09.html" > < strong aria-hidden = "true" > 7.9.< / strong > 示例: 表达式求值< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-10.html" > < strong aria-hidden = "true" > 7.10.< / strong > 类型断言< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-11.html" > < strong aria-hidden = "true" > 7.11.< / strong > 基于类型断言识别错误类型< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-12.html" > < strong aria-hidden = "true" > 7.12.< / strong > 通过类型断言查询接口< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-13.html" > < strong aria-hidden = "true" > 7.13.< / strong > 类型分支< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-14.html" > < strong aria-hidden = "true" > 7.14.< / strong > 示例: 基于标记的XML解码< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch7/ch7-15.html" > < strong aria-hidden = "true" > 7.15.< / strong > 补充几点< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8.html" > < strong aria-hidden = "true" > 8.< / strong > Goroutines和Channels< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-01.html" > < strong aria-hidden = "true" > 8.1.< / strong > Goroutines< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-02.html" > < strong aria-hidden = "true" > 8.2.< / strong > 示例: 并发的Clock服务< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-03.html" > < strong aria-hidden = "true" > 8.3.< / strong > 示例: 并发的Echo服务< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-04.html" > < strong aria-hidden = "true" > 8.4.< / strong > Channels< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-05.html" > < strong aria-hidden = "true" > 8.5.< / strong > 并发的循环< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-06.html" > < strong aria-hidden = "true" > 8.6.< / strong > 示例: 并发的Web爬虫< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-07.html" > < strong aria-hidden = "true" > 8.7.< / strong > 基于select的多路复用< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-08.html" > < strong aria-hidden = "true" > 8.8.< / strong > 示例: 并发的目录遍历< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-09.html" > < strong aria-hidden = "true" > 8.9.< / strong > 并发的退出< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch8/ch8-10.html" > < strong aria-hidden = "true" > 8.10.< / strong > 示例: 聊天服务< / a >
< / li >
< / ol >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9.html" > < strong aria-hidden = "true" > 9.< / strong > 基于共享变量的并发< / a >
< / li >
< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-01.html" > < strong aria-hidden = "true" > 9.1.< / strong > 竞争条件< / a >
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< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-02.html" > < strong aria-hidden = "true" > 9.2.< / strong > sync.Mutex互斥锁< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-03.html" > < strong aria-hidden = "true" > 9.3.< / strong > sync.RWMutex读写锁< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-04.html" > < strong aria-hidden = "true" > 9.4.< / strong > 内存同步< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-05.html" > < strong aria-hidden = "true" > 9.5.< / strong > sync.Once惰性初始化< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-06.html" > < strong aria-hidden = "true" > 9.6.< / strong > 竞争条件检测< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-07.html" > < strong aria-hidden = "true" > 9.7.< / strong > 示例: 并发的非阻塞缓存< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch9/ch9-08.html" > < strong aria-hidden = "true" > 9.8.< / strong > Goroutines和线程< / a >
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< / ol >
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< a href = "../ch10/ch10.html" > < strong aria-hidden = "true" > 10.< / strong > 包和工具< / a >
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< ol class = "section" >
< li class = "chapter-item expanded " >
< a href = "../ch10/ch10-01.html" > < strong aria-hidden = "true" > 10.1.< / strong > 包简介< / a >
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< li class = "chapter-item expanded " >
< a href = "../ch10/ch10-02.html" > < strong aria-hidden = "true" > 10.2.< / strong > 导入路径< / a >
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< li class = "chapter-item expanded " >
< a href = "../ch10/ch10-03.html" > < strong aria-hidden = "true" > 10.3.< / strong > 包声明< / a >
< / li >
< li class = "chapter-item expanded " >
< a href = "../ch10/ch10-04.html" > < strong aria-hidden = "true" > 10.4.< / strong > 导入声明< / a >
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< li class = "chapter-item expanded " >
< a href = "../ch10/ch10-05.html" class = "active" > < strong aria-hidden = "true" > 10.5.< / strong > 包的匿名导入< / a >
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< a href = "../ch10/ch10-06.html" > < strong aria-hidden = "true" > 10.6.< / strong > 包和命名< / a >
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< a href = "../ch10/ch10-07.html" > < strong aria-hidden = "true" > 10.7.< / strong > 工具< / a >
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< / ol >
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< a href = "../ch11/ch11.html" > < strong aria-hidden = "true" > 11.< / strong > 测试< / a >
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< a href = "../ch11/ch11-01.html" > < strong aria-hidden = "true" > 11.1.< / strong > go test< / a >
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< a href = "../ch11/ch11-02.html" > < strong aria-hidden = "true" > 11.2.< / strong > 测试函数< / a >
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< a href = "../ch11/ch11-03.html" > < strong aria-hidden = "true" > 11.3.< / strong > 测试覆盖率< / a >
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< a href = "../ch11/ch11-04.html" > < strong aria-hidden = "true" > 11.4.< / strong > 基准测试< / a >
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< a href = "../ch11/ch11-05.html" > < strong aria-hidden = "true" > 11.5.< / strong > 剖析< / a >
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< a href = "../ch11/ch11-06.html" > < strong aria-hidden = "true" > 11.6.< / strong > 示例函数< / a >
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< main >
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< ul dir = "auto" > < li > < em > 凹语言(Go实现, 面向WASM设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li > < li > < em > WaBook(Go语言实现的MD电子书构建工具): < a href = "https://github.com/wa-lang/wabook" > https://github.com/wa-lang/wabook< / a > < / em > < / li > < / ul > < hr >
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< h2 > 10.5. 包的匿名导入< / h2 >
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< p > 如果只是导入一个包而并不使用导入的包将会导致一个编译错误。但是有时候我们只是想利用导入包而产生的副作用： （ ） ， < code > _< / code > 来重命名导入的包。像往常一样，下划线< code > _< / code > 为空白标识符，并不能被访问。< / p >
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< pre > < code class = "language-Go" > import _ " image/png" // register PNG decoder
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< / code > < / pre >
< p > 这个被称为包的匿名导入。它通常是用来实现一个编译时机制， ， ， < / p >
< p > 标准库的image图像包包含了一个< code > Decode< / code > 函数，用于从< code > io.Reader< / code > 接口读取数据并解码图像， ， < code > image.Decode< / code > 很容易编写一个图像格式的转换工具，读取一种格式的图像，然后编码为另一种图像格式：< / p >
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< p > <!-- raw HTML omitted --> <!-- raw HTML omitted --> gopl.io/ch10/jpeg<!-- raw HTML omitted --> <!-- raw HTML omitted --> < / p >
< pre > < code class = "language-Go" > // The jpeg command reads a PNG image from the standard input
// and writes it as a JPEG image to the standard output.
package main
import (
" fmt"
" image"
" image/jpeg"
_ " image/png" // register PNG decoder
" io"
" os"
)
func main() {
if err := toJPEG(os.Stdin, os.Stdout); err != nil {
fmt.Fprintf(os.Stderr, " jpeg: %v\n" , err)
os.Exit(1)
}
}
func toJPEG(in io.Reader, out io.Writer) error {
img, kind, err := image.Decode(in)
if err != nil {
return err
}
fmt.Fprintln(os.Stderr, " Input format =" , kind)
return jpeg.Encode(out, img, & jpeg.Options{Quality: 95})
}
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< / code > < / pre >
< p > 如果我们将< code > gopl.io/ch3/mandelbrot< / code > （ ） ， ， （ < / p >
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< pre > < code > $ go build gopl.io/ch3/mandelbrot
$ go build gopl.io/ch10/jpeg
$ ./mandelbrot | ./jpeg > mandelbrot.jpg
Input format = png
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< / code > < / pre >
< p > 要注意image/png包的匿名导入语句。如果没有这一行语句， ， ： < / p >
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< pre > < code > $ go build gopl.io/ch10/jpeg
$ ./mandelbrot | ./jpeg > mandelbrot.jpg
jpeg: image: unknown format
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< / code > < / pre >
< p > 下面的代码演示了它的工作机制。标准库还提供了GIF、PNG和JPEG等格式图像的解码器， ， ， ， ： ； ， ； ； ， ， ： < / p >
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< pre > < code class = "language-Go" > package png // image/png
func Decode(r io.Reader) (image.Image, error)
func DecodeConfig(r io.Reader) (image.Config, error)
func init() {
const pngHeader = " \x89PNG\r\n\x1a\n"
image.RegisterFormat(" png" , pngHeader, Decode, DecodeConfig)
}
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< / code > < / pre >
< p > 最终的效果是， < / p >
< p > 数据库包database/sql也是采用了类似的技术， ： < / p >
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< pre > < code class = "language-Go" > import (
" database/sql"
_ " github.com/lib/pq" // enable support for Postgres
_ " github.com/go-sql-driver/mysql" // enable support for MySQL
)
db, err = sql.Open(" postgres" , dbname) // OK
db, err = sql.Open(" mysql" , dbname) // OK
db, err = sql.Open(" sqlite3" , dbname) // returns error: unknown driver " sqlite3"
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< / code > < / pre >
< p > < strong > 练习 10.1： < / strong > 扩展jpeg程序， ， ， < / p >
< p > < strong > 练习 10.2： < / strong > 设计一个通用的压缩文件读取框架， （ ） （ ） ， < / p >
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