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< 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.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" class = "active" > < 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< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < s
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
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< h2 id = "25-类型" > < a class = "header" href = "#25-类型" > 2.5. 类型< / a > < / h2 >
< p > 变量或表达式的类型定义了对应存储值的属性特征， （ ） ， ， ， < / p >
< p > 在任何程序中都会存在一些变量有着相同的内部结构， ， ； ； < / p >
< p > 一个类型声明语句创建了一个新的类型名称，和现有类型具有相同的底层结构。新命名的类型提供了一个方法，用来分隔不同概念的类型，这样即使它们底层类型相同也是不兼容的。< / p >
< pre > < code class = "language-Go" > type 类型名字 底层类型
< / code > < / pre >
< p > 类型声明语句一般出现在包一级，因此如果新创建的类型名字的首字符大写，则在包外部也可以使用。< / p >
< p > 译注： ， ， ； ， ， < a href = "https://github.com/golang/go/issues/5763" > Issue763< / a > 的回复：< / p >
< blockquote >
< p > A solution that's been kicking around for a while:< / p >
< p > For Go 2 (can't do it before then): Change the definition to “lower case letters and _ are package-local; all else is exported”. Then with non-cased languages, such as Japanese, we can write 日本语 for an exported name and _日本语 for a local name. This rule has no effect, relative to the Go 1 rule, with cased languages. They behave exactly the same.< / p >
< / blockquote >
< p > 为了说明类型声明，我们将不同温度单位分别定义为不同的类型：< / p >
< p > < u > < i > gopl.io/ch2/tempconv0< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Package tempconv performs Celsius and Fahrenheit temperature computations.
package tempconv
import " fmt"
type Celsius float64 // 摄氏温度
type Fahrenheit float64 // 华氏温度
const (
AbsoluteZeroC Celsius = -273.15 // 绝对零度
FreezingC Celsius = 0 // 结冰点温度
BoilingC Celsius = 100 // 沸水温度
)
func CToF(c Celsius) Fahrenheit { return Fahrenheit(c*9/5 + 32) }
func FToC(f Fahrenheit) Celsius { return Celsius((f - 32) * 5 / 9) }
< / code > < / pre >
< p > 我们在这个包声明了两种类型： ， ， ， ； ， ， ， ， < / p >
< p > 对于每一个类型T， ， （ ： ， ， < code > (*int)(0)< / code > ） ， ， ， ， ， < / p >
< p > 数值类型之间的转型也是允许的， ， ， ， < code > []byte< / code > 类型的slice将拷贝一个字符串数据的副本。在任何情况下， （ < / p >
< p > 底层数据类型决定了内部结构和表达方式， ， ， < / p >
< pre > < code class = "language-Go" > fmt.Printf(" %g\n" , BoilingC-FreezingC) // " 100" °C
boilingF := CToF(BoilingC)
fmt.Printf(" %g\n" , boilingF-CToF(FreezingC)) // " 180" °F
fmt.Printf(" %g\n" , boilingF-FreezingC) // compile error: type mismatch
< / code > < / pre >
< p > 比较运算符< code > ==< / code > 和< code > < < / code > 也可以用来比较一个命名类型的变量和另一个有相同类型的变量，或有着相同底层类型的未命名类型的值之间做比较。但是如果两个值有着不同的类型，则不能直接进行比较：< / p >
< pre > < code class = "language-Go" > var c Celsius
var f Fahrenheit
fmt.Println(c == 0) // " true"
fmt.Println(f > = 0) // " true"
fmt.Println(c == f) // compile error: type mismatch
fmt.Println(c == Celsius(f)) // " true" !
< / code > < / pre >
< p > 注意最后那个语句。尽管看起来像函数调用， ， ， < / p >
< p > 一个命名的类型可以提供书写方便， （ ： ） ， ， < / p >
< p > 命名类型还可以为该类型的值定义新的行为。这些行为表示为一组关联到该类型的函数集合，我们称为类型的方法集。我们将在第六章中讨论方法的细节，这里只说些简单用法。< / p >
< p > 下面的声明语句， ， ， ： < / p >
< pre > < code class = "language-Go" > func (c Celsius) String() string { return fmt.Sprintf(" %g°C" , c) }
< / code > < / pre >
< p > 许多类型都会定义一个String方法， ， ， < / p >
< pre > < code class = "language-Go" > c := FToC(212.0)
fmt.Println(c.String()) // " 100°C"
fmt.Printf(" %v\n" , c) // " 100°C" ; no need to call String explicitly
fmt.Printf(" %s\n" , c) // " 100°C"
fmt.Println(c) // " 100°C"
fmt.Printf(" %g\n" , c) // " 100" ; does not call String
fmt.Println(float64(c)) // " 100" ; does not call String
< / code > < / pre >
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