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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" > < 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" > < strong aria-hidd
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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 = "63-通过嵌入结构体来扩展类型" > < a class = "header" href = "#63-通过嵌入结构体来扩展类型" > 6.3. 通过嵌入结构体来扩展类型< / a > < / h2 >
< p > 来看看ColoredPoint这个类型： < / p >
< p > < u > < i > gopl.io/ch6/coloredpoint< / i > < / u > < / p >
< pre > < code class = "language-go" > import " image/color"
type Point struct{ X, Y float64 }
type ColoredPoint struct {
Point
Color color.RGBA
}
< / code > < / pre >
< p > 我们完全可以将ColoredPoint定义为一个有三个字段的struct， ， ， ， ， ， ， < / p >
< pre > < code class = "language-go" > var cp ColoredPoint
cp.X = 1
fmt.Println(cp.Point.X) // " 1"
cp.Point.Y = 2
fmt.Println(cp.Y) // " 2"
< / code > < / pre >
< p > 对于Point中的方法我们也有类似的用法， ， ： < / p >
< pre > < code class = "language-go" > red := color.RGBA{255, 0, 0, 255}
blue := color.RGBA{0, 0, 255, 255}
var p = ColoredPoint{Point{1, 1}, red}
var q = ColoredPoint{Point{5, 4}, blue}
fmt.Println(p.Distance(q.Point)) // " 5"
p.ScaleBy(2)
q.ScaleBy(2)
fmt.Println(p.Distance(q.Point)) // " 10"
< / code > < / pre >
< p > Point类的方法也被引入了ColoredPoint。用这种方式， ， ， ， < / p >
< p > 读者如果对基于类来实现面向对象的语言比较熟悉的话， ， ， " is a" Point类型。但这是错误的理解。请注意上面例子中对Distance方法的调用。Distance有一个参数是Point类型， ， ， ： < / p >
< pre > < code class = "language-go" > p.Distance(q) // compile error: cannot use q (ColoredPoint) as Point
< / code > < / pre >
< p > 一个ColoredPoint并不是一个Point， " has a" Point， ， ， ： < / p >
< pre > < code class = "language-go" > func (p ColoredPoint) Distance(q Point) float64 {
return p.Point.Distance(q)
}
func (p *ColoredPoint) ScaleBy(factor float64) {
p.Point.ScaleBy(factor)
}
< / code > < / pre >
< p > 当Point.Distance被第一个包装方法调用时， ， ， ， ， < / p >
< p > 在类型中内嵌的匿名字段也可能是一个命名类型的指针， （ ： ） < / p >
< pre > < code class = "language-go" > type ColoredPoint struct {
*Point
Color color.RGBA
}
p := ColoredPoint{& Point{1, 1}, red}
q := ColoredPoint{& Point{5, 4}, blue}
fmt.Println(p.Distance(*q.Point)) // " 5"
q.Point = p.Point // p and q now share the same Point
p.ScaleBy(2)
fmt.Println(*p.Point, *q.Point) // " {2 2} {2 2}"
< / code > < / pre >
< p > 一个struct类型也可能会有多个匿名字段。我们将ColoredPoint定义为下面这样： < / p >
< pre > < code class = "language-go" > type ColoredPoint struct {
Point
color.RGBA
}
< / code > < / pre >
< p > 然后这种类型的值便会拥有Point和RGBA类型的所有方法， ， ， ， ， ， ， < / p >
< p > 方法只能在命名类型（ ） ， ， < / p >
2022-09-06 12:13:56 +00:00
< p > 下面是一个小trick。这个例子展示了简单的cache， ， （ ） ： < / p >
2022-08-04 06:59:33 +00:00
< pre > < code class = "language-go" > var (
mu sync.Mutex // guards mapping
mapping = make(map[string]string)
)
func Lookup(key string) string {
mu.Lock()
v := mapping[key]
mu.Unlock()
return v
}
< / code > < / pre >
< p > 下面这个版本在功能上是一致的， ： < / p >
< pre > < code class = "language-go" > var cache = struct {
sync.Mutex
mapping map[string]string
}{
mapping: make(map[string]string),
}
func Lookup(key string) string {
cache.Lock()
v := cache.mapping[key]
cache.Unlock()
return v
}
< / code > < / pre >
< p > 我们给新的变量起了一个更具表达性的名字： ， ， < / p >
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