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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 >
< li class = "chapter-item expanded " >
< a href = "../ch5/ch5.html" > < strong aria-hidden = "true" > 5.< / strong > 函数< / a >
< / li >
< ol class = "section" >
< 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 >
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< 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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< 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 >
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< a href = "../ch10/ch10-04.html" > < strong aria-hidden = "true" > 10.4.< / strong > 导入声明< / a >
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< a href = "../ch10/ch10-05.html" > < 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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< a href = "../ch12/ch12.html" > < strong aria-hidden = "true" > 12.< / strong > 反射< / a >
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< a href = "../ch12/ch12-05.html" > < strong aria-hidden = "true" > 12.5.< / strong > 通过reflect.Value修改值< / a >
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< li class = "chapter-item expanded " >
< a href = "../ch12/ch12-06.html" > < strong aria-hidden = "true" > 12.6.< / strong > 示例: 解码S表达式< / a >
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< a href = "../ch12/ch12-07.html" class = "active" > < strong aria-hidden = "true" > 12.7.< / strong > 获取结构体字段标签< / a >
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< a href = "../ch12/ch12-08.html" > < strong aria-hidden = "true" > 12.8.< / strong > 显示一个类型的方法集< / 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 > 12.7. 获取结构体字段标签< / h2 >
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< p > 在4.5节我们使用构体成员标签用于设置对应JSON对应的名字。其中json成员标签让我们可以选择成员的名字和抑制零值成员的输出。在本节， < / p >
< p > 对于一个web服务， ， ， < / p >
< p > 首先， ， ， ， < / p >
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< p > <!-- raw HTML omitted --> <!-- raw HTML omitted --> gopl.io/ch12/search<!-- raw HTML omitted --> <!-- raw HTML omitted --> < / p >
< pre > < code class = "language-Go" > import " gopl.io/ch12/params"
// search implements the /search URL endpoint.
func search(resp http.ResponseWriter, req *http.Request) {
var data struct {
Labels []string `http:" l" `
MaxResults int `http:" max" `
Exact bool `http:" x" `
}
data.MaxResults = 10 // set default
if err := params.Unpack(req, & data); err != nil {
http.Error(resp, err.Error(), http.StatusBadRequest) // 400
return
}
// ...rest of handler...
fmt.Fprintf(resp, " Search: %+v\n" , data)
}
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< / code > < / pre >
< p > 下面的Unpack函数主要完成三件事情。第一， ， ， < / p >
< p > 下一步， ， ， ， ， " ..." 形式的子串。< / p >
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< p > <!-- raw HTML omitted --> <!-- raw HTML omitted --> gopl.io/ch12/params<!-- raw HTML omitted --> <!-- raw HTML omitted --> < / p >
< pre > < code class = "language-Go" > // Unpack populates the fields of the struct pointed to by ptr
// from the HTTP request parameters in req.
func Unpack(req *http.Request, ptr interface{}) error {
if err := req.ParseForm(); err != nil {
return err
}
// Build map of fields keyed by effective name.
fields := make(map[string]reflect.Value)
v := reflect.ValueOf(ptr).Elem() // the struct variable
for i := 0; i < v.NumField(); i++ {
fieldInfo := v.Type().Field(i) // a reflect.StructField
tag := fieldInfo.Tag // a reflect.StructTag
name := tag.Get(" http" )
if name == " " {
name = strings.ToLower(fieldInfo.Name)
}
fields[name] = v.Field(i)
}
// Update struct field for each parameter in the request.
for name, values := range req.Form {
f := fields[name]
if !f.IsValid() {
continue // ignore unrecognized HTTP parameters
}
for _, value := range values {
if f.Kind() == reflect.Slice {
elem := reflect.New(f.Type().Elem()).Elem()
if err := populate(elem, value); err != nil {
return fmt.Errorf(" %s: %v" , name, err)
}
f.Set(reflect.Append(f, elem))
} else {
if err := populate(f, value); err != nil {
return fmt.Errorf(" %s: %v" , name, err)
}
}
}
}
return nil
}
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< / code > < / pre >
< p > 最后， ， ， ， ， ， ， < / p >
< p > populate函数小心用请求的字符串类型参数值来填充单一的成员v（ ） ， < / p >
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< pre > < code class = "language-Go" > func populate(v reflect.Value, value string) error {
switch v.Kind() {
case reflect.String:
v.SetString(value)
case reflect.Int:
i, err := strconv.ParseInt(value, 10, 64)
if err != nil {
return err
}
v.SetInt(i)
case reflect.Bool:
b, err := strconv.ParseBool(value)
if err != nil {
return err
}
v.SetBool(b)
default:
return fmt.Errorf(" unsupported kind %s" , v.Type())
}
return nil
}
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< / code > < / pre >
< p > 如果我们上上面的处理程序添加到一个web服务器， ： < / p >
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< pre > < code > $ go build gopl.io/ch12/search
$ ./search &
$ ./fetch 'http://localhost:12345/search'
Search: {Labels:[] MaxResults:10 Exact:false}
$ ./fetch 'http://localhost:12345/search?l=golang& l=programming'
Search: {Labels:[golang programming] MaxResults:10 Exact:false}
$ ./fetch 'http://localhost:12345/search?l=golang& l=programming& max=100'
Search: {Labels:[golang programming] MaxResults:100 Exact:false}
$ ./fetch 'http://localhost:12345/search?x=true& l=golang& l=programming'
Search: {Labels:[golang programming] MaxResults:10 Exact:true}
$ ./fetch 'http://localhost:12345/search?q=hello& x=123'
x: strconv.ParseBool: parsing " 123" : invalid syntax
$ ./fetch 'http://localhost:12345/search?q=hello& max=lots'
max: strconv.ParseInt: parsing " lots" : invalid syntax
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< / code > < / pre >
< p > < strong > 练习 12.11： < / strong > 编写相应的Pack函数， ， < / p >
< p > < strong > 练习 12.12： < / strong > 扩展成员标签以表示一个请求参数的有效值规则。例如， ， < / p >
< p > < strong > 练习 12.13： < / strong > 修改S表达式的编码器（ ） （ ） ， （ ） " ..." 字串。< / p >
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