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2023-06-26 17:30:52 +00:00
< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < 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 > < 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 > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < 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 > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < 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 > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < 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< /
2022-08-04 06:59:33 +00:00
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2024-06-12 07:20:07 +00:00
< li > < em > Go语言圣经读书笔记(挖坑中...): < a href = "https://github.com/chai2010/gopl-notes-zh" > https://github.com/chai2010/gopl-notes-zh< / a > < / em > < / li >
< 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 >
2023-06-26 17:46:27 +00:00
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2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "712-通过类型断言询问行为" > < a class = "header" href = "#712-通过类型断言询问行为" > 7.12. 通过类型断言询问行为< / a > < / h2 >
< p > 下面这段逻辑和net/http包中web服务器负责写入HTTP头字段（ ： " Content-type:text/html" ） ； < / p >
< pre > < code class = "language-go" > func writeHeader(w io.Writer, contentType string) error {
if _, err := w.Write([]byte(" Content-Type: " )); err != nil {
return err
}
if _, err := w.Write([]byte(contentType)); err != nil {
return err
}
// ...
}
< / code > < / pre >
< p > 因为Write方法需要传入一个byte切片而我们希望写入的值是一个字符串， ， ？ < / p >
< p > 这个io.Writer接口告诉我们关于w持有的具体类型的唯一东西： ， ； （ ， ， < code > *bytes.Buffer< / code > ， < code > *os.File< / code > 和< code > *bufio.Writer< / code > 。）< / p >
< p > 我们不能对任意io.Writer类型的变量w， < / p >
< pre > < code class = "language-go" > // writeString writes s to w.
// If w has a WriteString method, it is invoked instead of w.Write.
func writeString(w io.Writer, s string) (n int, err error) {
type stringWriter interface {
WriteString(string) (n int, err error)
}
if sw, ok := w.(stringWriter); ok {
return sw.WriteString(s) // avoid a copy
}
return w.Write([]byte(s)) // allocate temporary copy
}
func writeHeader(w io.Writer, contentType string) error {
if _, err := writeString(w, " Content-Type: " ); err != nil {
return err
}
if _, err := writeString(w, contentType); err != nil {
return err
}
// ...
}
< / code > < / pre >
< p > 为了避免重复定义， ， < / p >
< p > 这个例子的神奇之处在于， ， ， ， ： ， < / p >
< pre > < code class = "language-go" > interface {
io.Writer
WriteString(s string) (n int, err error)
}
< / code > < / pre >
< p > 尽管io.WriteString实施了这个假设， ， ， ， < / p >
< p > 上面的writeString函数使用一个类型断言来获知一个普遍接口类型的值是否满足一个更加具体的接口类型； ， ， ， < / p >
< p > 这也是fmt.Fprintf函数怎么从其它所有值中区分满足error或者fmt.Stringer接口的值。在fmt.Fprintf内部， ， ： < / p >
< pre > < code class = "language-go" > package fmt
func formatOneValue(x interface{}) string {
if err, ok := x.(error); ok {
return err.Error()
}
if str, ok := x.(Stringer); ok {
return str.String()
}
// ...all other types...
}
< / code > < / pre >
< p > 如果x满足这两个接口类型中的一个， ， ； < / p >
< p > 再一次的， ， < / p >
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