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2023-03-31 10:23:29 +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.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
2022-08-04 06:59:33 +00:00
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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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< hr >
< h2 id = "133-示例-深度相等判断" > < a class = "header" href = "#133-示例-深度相等判断" > 13.3. 示例: 深度相等判断< / a > < / h2 >
< p > 来自reflect包的DeepEqual函数可以对两个值进行深度相等判断。DeepEqual函数使用内建的==比较操作符对基础类型进行相等判断,对于复合类型则递归该变量的每个基础类型然后做类似的比较判断。因为它可以工作在任意的类型上,甚至对于一些不支持==操作运算符的类型也可以工作, 因此在一些测试代码中广泛地使用该函数。比如下面的代码是用DeepEqual函数比较两个字符串slice是否相等。< / p >
< pre > < code class = "language-Go" > func TestSplit(t *testing.T) {
got := strings.Split(" a:b:c" , " :" )
want := []string{" a" , " b" , " c" };
if !reflect.DeepEqual(got, want) { /* ... */ }
}
< / code > < / pre >
< p > 尽管DeepEqual函数很方便, 而且可以支持任意的数据类型, 但是它也有不足之处。例如, 它将一个nil值的map和非nil值但是空的map视作不相等, 同样nil值的slice 和非nil但是空的slice也视作不相等。< / p >
< pre > < code class = "language-Go" > var a, b []string = nil, []string{}
fmt.Println(reflect.DeepEqual(a, b)) // " false"
var c, d map[string]int = nil, make(map[string]int)
fmt.Println(reflect.DeepEqual(c, d)) // " false"
< / code > < / pre >
< p > 我们希望在这里实现一个自己的Equal函数, 用于比较类型的值。和DeepEqual函数类似的地方是它也是基于slice和map的每个元素进行递归比较, 不同之处是它将nil值的slice( map类似) 和非nil值但是空的slice视作相等的值。基础部分的比较可以基于reflect包完成, 和12.3章的Display函数的实现方法类似。同样, 我们也定义了一个内部函数equal, 用于内部的递归比较。读者目前不用关心seen参数的具体含义。对于每一对需要比较的x和y, equal函数首先检测它们是否都有效( 或都无效) , 然后检测它们是否是相同的类型。剩下的部分是一个巨大的switch分支, 用于相同基础类型的元素比较。因为页面空间的限制, 我们省略了一些相似的分支。< / p >
< p > < u > < i > gopl.io/ch13/equal< / i > < / u > < / p >
< pre > < code class = "language-Go" > func equal(x, y reflect.Value, seen map[comparison]bool) bool {
if !x.IsValid() || !y.IsValid() {
return x.IsValid() == y.IsValid()
}
if x.Type() != y.Type() {
return false
}
// ...cycle check omitted (shown later)...
switch x.Kind() {
case reflect.Bool:
return x.Bool() == y.Bool()
case reflect.String:
return x.String() == y.String()
// ...numeric cases omitted for brevity...
case reflect.Chan, reflect.UnsafePointer, reflect.Func:
return x.Pointer() == y.Pointer()
case reflect.Ptr, reflect.Interface:
return equal(x.Elem(), y.Elem(), seen)
case reflect.Array, reflect.Slice:
if x.Len() != y.Len() {
return false
}
for i := 0; i < x.Len(); i++ {
if !equal(x.Index(i), y.Index(i), seen) {
return false
}
}
return true
// ...struct and map cases omitted for brevity...
}
panic(" unreachable" )
}
< / code > < / pre >
< p > 和前面的建议一样, 我们并不公开reflect包相关的接口, 所以导出的函数需要在内部自己将变量转为reflect.Value类型。< / p >
< pre > < code class = "language-Go" > // Equal reports whether x and y are deeply equal.
func Equal(x, y interface{}) bool {
seen := make(map[comparison]bool)
return equal(reflect.ValueOf(x), reflect.ValueOf(y), seen)
}
type comparison struct {
x, y unsafe.Pointer
t reflect.Type
}
< / code > < / pre >
< p > 为了确保算法对于有环的数据结构也能正常退出, 我们必须记录每次已经比较的变量, 从而避免进入第二次的比较。Equal函数分配了一组用于比较的结构体, 包含每对比较对象的地址( unsafe.Pointer形式保存) 和类型。我们要记录类型的原因是, 有些不同的变量可能对应相同的地址。例如, 如果x和y都是数组类型, 那么x和x[0]将对应相同的地址, y和y[0]也是对应相同的地址, 这可以用于区分x与y之间的比较或x[0]与y[0]之间的比较是否进行过了。< / p >
< pre > < code class = "language-Go" > // cycle check
if x.CanAddr() & & y.CanAddr() {
xptr := unsafe.Pointer(x.UnsafeAddr())
yptr := unsafe.Pointer(y.UnsafeAddr())
if xptr == yptr {
return true // identical references
}
c := comparison{xptr, yptr, x.Type()}
if seen[c] {
return true // already seen
}
seen[c] = true
}
< / code > < / pre >
< p > 这是Equal函数用法的例子:< / p >
< pre > < code class = "language-Go" > fmt.Println(Equal([]int{1, 2, 3}, []int{1, 2, 3})) // " true"
fmt.Println(Equal([]string{" foo" }, []string{" bar" })) // " false"
fmt.Println(Equal([]string(nil), []string{})) // " true"
fmt.Println(Equal(map[string]int(nil), map[string]int{})) // " true"
< / code > < / pre >
< p > Equal函数甚至可以处理类似12.3章中导致Display陷入死循环的带有环的数据。< / p >
< pre > < code class = "language-Go" > // Circular linked lists a -> b -> a and c -> c.
type link struct {
value string
tail *link
}
a, b, c := & link{value: " a" }, & link{value: " b" }, & link{value: " c" }
a.tail, b.tail, c.tail = b, a, c
fmt.Println(Equal(a, a)) // " true"
fmt.Println(Equal(b, b)) // " true"
fmt.Println(Equal(c, c)) // " true"
fmt.Println(Equal(a, b)) // " false"
fmt.Println(Equal(a, c)) // " false"
< / code > < / pre >
< p > < strong > 练习 13.1: < / strong > 定义一个深比较函数,对于十亿以内的数字比较,忽略类型差异。< / p >
< p > < strong > 练习 13.2: < / strong > 编写一个函数,报告其参数是否为循环数据结构。< / p >
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