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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 >
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "713-类型分支" > < a class = "header" href = "#713-类型分支" > 7.13. 类型分支< / a > < / h2 >
< p > 接口被以两种不同的方式使用。在第一个方式中， ， ， ， ， ， ， ， < / p >
< p > 第二个方式是利用一个接口值可以持有各种具体类型值的能力， ， ， ， （ ） ， （ ） < / p >
< p > 如果你熟悉面向对象编程， （ ） （ ） ， ， < / p >
< p > 和其它那些语言一样， ： < / p >
< pre > < code class = "language-go" > import " database/sql"
func listTracks(db sql.DB, artist string, minYear, maxYear int) {
result, err := db.Exec(
" SELECT * FROM tracks WHERE artist = ? AND ? < = year AND year < = ?" ,
artist, minYear, maxYear)
// ...
}
< / code > < / pre >
< p > Exec方法使用SQL字面量替换在查询字符串中的每个'?'； ， ， ， ， ； ， ， < / p >
< pre > < code class = "language-go" > func sqlQuote(x interface{}) string {
if x == nil {
return " NULL"
} else if _, ok := x.(int); ok {
return fmt.Sprintf(" %d" , x)
} else if _, ok := x.(uint); ok {
return fmt.Sprintf(" %d" , x)
} else if b, ok := x.(bool); ok {
if b {
return " TRUE"
}
return " FALSE"
} else if s, ok := x.(string); ok {
return sqlQuoteString(s) // (not shown)
} else {
panic(fmt.Sprintf(" unexpected type %T: %v" , x, x))
}
}
< / code > < / pre >
< p > switch语句可以简化if-else链， （ ） < / p >
< p > 在最简单的形式中， ， ， ： < / p >
< pre > < code class = "language-go" > switch x.(type) {
case nil: // ...
case int, uint: // ...
case bool: // ...
case string: // ...
default: // ...
}
< / code > < / pre >
< p > 和（ ） ， ， ， ， ， < / p >
< p > 注意到在原来的函数中， ， ， < / p >
< pre > < code class = "language-go" > switch x := x.(type) { /* ... */ }
< / code > < / pre >
< p > 这里我们已经将新的变量也命名为x； ， ， ， < / p >
< p > 使用类型分支的扩展形式来重写sqlQuote函数会让这个函数更加的清晰： < / p >
< pre > < code class = "language-go" > func sqlQuote(x interface{}) string {
switch x := x.(type) {
case nil:
return " NULL"
case int, uint:
return fmt.Sprintf(" %d" , x) // x has type interface{} here.
case bool:
if x {
return " TRUE"
}
return " FALSE"
case string:
return sqlQuoteString(x) // (not shown)
default:
panic(fmt.Sprintf(" unexpected type %T: %v" , x, x))
}
}
< / code > < / pre >
< p > 在这个版本的函数中， ， ， ， （ ） ； ， ， < / p >
< p > 尽管sqlQuote接受一个任意类型的参数， ； ， ， ， ， ， （ ） < / p >
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