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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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2023-06-26 17:46:27 +00:00
< li > < em > 凹语言(专为 WebAssembly 设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
< li > < em > KCL 配置语言(Rust): < a href = "https://github.com/kcl-lang/kcl" > https://github.com/kcl-lang/kcl< / a > < / em > < / li >
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2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "71-接口约定" > < a class = "header" href = "#71-接口约定" > 7.1. 接口约定< / a > < / h2 >
< p > 目前为止，我们看到的类型都是具体的类型。一个具体的类型可以准确的描述它所代表的值，并且展示出对类型本身的一些操作方式：就像数字类型的算术操作，切片类型的取下标、添加元素和范围获取操作。具体的类型还可以通过它的内置方法提供额外的行为操作。总的来说，当你拿到一个具体的类型时你就知道它的本身是什么和你可以用它来做什么。< / p >
< p > 在Go语言中还存在着另外一种类型： ； ， ， < / p >
< p > 在本书中， ： ， ， ， ， ， < / p >
< pre > < code class = "language-go" > package fmt
func Fprintf(w io.Writer, format string, args ...interface{}) (int, error)
func Printf(format string, args ...interface{}) (int, error) {
return Fprintf(os.Stdout, format, args...)
}
func Sprintf(format string, args ...interface{}) string {
var buf bytes.Buffer
Fprintf(& buf, format, args...)
return buf.String()
}
< / code > < / pre >
< p > Fprintf的前缀F表示文件（ ） < code > *os.File< / code > 类型； & buf是一个指向可以写入字节的内存缓冲区，
并不是一个文件类型尽管它在某种意义上和文件类型相似。< / p >
< p > 即使Fprintf函数中的第一个参数也不是一个文件类型。它是io.Writer类型， ： < / p >
< pre > < code class = "language-go" > package io
// Writer is the interface that wraps the basic Write method.
type Writer interface {
// Write writes len(p) bytes from p to the underlying data stream.
// It returns the number of bytes written from p (0 < = n < = len(p))
// and any error encountered that caused the write to stop early.
// Write must return a non-nil error if it returns n < len(p).
// Write must not modify the slice data, even temporarily.
//
// Implementations must not retain p.
Write(p []byte) (n int, err error)
}
< / code > < / pre >
< p > io.Writer类型定义了函数Fprintf和这个函数调用者之间的约定。一方面这个约定需要调用者提供具体类型的值就像< code > *os.File< / code > 和< code > *bytes.Buffer< / code > ， ， < / p >
< p > 因为fmt.Fprintf函数没有对具体操作的值做任何假设， ， ， （ ） < / p >
< p > 让我们通过一个新的类型来进行校验，下面< code > *ByteCounter< / code > 类型里的Write方法， （ ， < code > *c< / code > 的类型匹配的转换是必须的。）< / p >
< p > < u > < i > gopl.io/ch7/bytecounter< / i > < / u > < / p >
< pre > < code class = "language-go" > type ByteCounter int
func (c *ByteCounter) Write(p []byte) (int, error) {
*c += ByteCounter(len(p)) // convert int to ByteCounter
return len(p), nil
}
< / code > < / pre >
< p > 因为*ByteCounter满足io.Writer的约定， ； < / p >
< pre > < code class = "language-go" > var c ByteCounter
c.Write([]byte(" hello" ))
fmt.Println(c) // " 5" , = len(" hello" )
c = 0 // reset the counter
var name = " Dolly"
fmt.Fprintf(& c, " hello, %s" , name)
fmt.Println(c) // " 12" , = len(" hello, Dolly" )
< / code > < / pre >
< p > 除了io.Writer这个接口类型， ， " 100°C" ， ， " {1 2 3}" 。给一个类型定义String方法， ： < / p >
< pre > < code class = "language-go" > package fmt
// The String method is used to print values passed
// as an operand to any format that accepts a string
// or to an unformatted printer such as Print.
type Stringer interface {
String() string
}
< / code > < / pre >
< p > 我们会在7.10节解释fmt包怎么发现哪些值是满足这个接口类型的。< / p >
< p > < strong > 练习 7.1： < / strong > 使用来自ByteCounter的思路， < / p >
< p > < strong > 练习 7.2： < / strong > 写一个带有如下函数签名的函数CountingWriter， ， < / p >
< pre > < code class = "language-go" > func CountingWriter(w io.Writer) (io.Writer, *int64)
< / code > < / pre >
< p > < strong > 练习 7.3： < / strong > 为在gopl.io/ch4/treesort（ < / p >
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