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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" class = "active" > < 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.<
2022-08-04 06:59:33 +00:00
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2024-06-12 07:20:07 +00:00
< li > < em > Go语言圣经读书笔记(挖坑中...): < a href = "https://github.com/chai2010/gopl-notes-zh" > https://github.com/chai2010/gopl-notes-zh< / a > < / em > < / li >
< li > < em > 凹语言(Go实现, 面向WASM设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2023-06-26 17:46:27 +00:00
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "42-slice" > < a class = "header" href = "#42-slice" > 4.2. Slice< / a > < / h2 >
< p > Slice（ ） ， ， ； ， < / p >
< p > 数组和slice之间有着紧密的联系。一个slice是一个轻量级的数据结构， （ ） ， ： ， ； ， < / p >
< p > 多个slice之间可以共享底层的数据， ， < / p >
< pre > < code class = "language-Go" > months := [...]string{1: " January" , /* ... */, 12: " December" }
< / code > < / pre >
< p > 因此一月份是months[1]， ， ， ， ， < / p >
< p > slice的切片操作s[i:j]， ， ， ， ， ， ； ， ： < / p >
< p > < img src = "../images/ch4-01.png" alt = "" / > < / p >
< pre > < code class = "language-Go" > Q2 := months[4:7]
summer := months[6:9]
fmt.Println(Q2) // [" April" " May" " June" ]
fmt.Println(summer) // [" June" " July" " August" ]
< / code > < / pre >
< p > 两个slice都包含了六月份， （ ） ： < / p >
< pre > < code class = "language-Go" > for _, s := range summer {
for _, q := range Q2 {
if s == q {
fmt.Printf(" %s appears in both\n" , s)
}
}
}
< / code > < / pre >
< p > 如果切片操作超出cap(s)的上限将导致一个panic异常， ， ： < / p >
< pre > < code class = "language-Go" > fmt.Println(summer[:20]) // panic: out of range
endlessSummer := summer[:5] // extend a slice (within capacity)
fmt.Println(endlessSummer) // " [June July August September October]"
< / code > < / pre >
< p > 另外，字符串的切片操作和[]byte字节类型切片的切片操作是类似的。都写作x[m:n]， ， ， ， < / p >
< p > 因为slice值包含指向第一个slice元素的指针， ， （ ） ， < / p >
< p > < u > < i > gopl.io/ch4/rev< / i > < / u > < / p >
< pre > < code class = "language-Go" > // reverse reverses a slice of ints in place.
func reverse(s []int) {
for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
s[i], s[j] = s[j], s[i]
}
}
< / code > < / pre >
< p > 这里我们反转数组的应用：< / p >
< pre > < code class = "language-Go" > a := [...]int{0, 1, 2, 3, 4, 5}
reverse(a[:])
fmt.Println(a) // " [5 4 3 2 1 0]"
< / code > < / pre >
< p > 一种将slice元素循环向左旋转n个元素的方法是三次调用reverse反转函数， ， ， （ ， ） < / p >
< pre > < code class = "language-Go" > s := []int{0, 1, 2, 3, 4, 5}
// Rotate s left by two positions.
reverse(s[:2])
reverse(s[2:])
reverse(s)
fmt.Println(s) // " [2 3 4 5 0 1]"
< / code > < / pre >
< p > 要注意的是slice类型的变量s和数组类型的变量a的初始化语法的差异。slice和数组的字面值语法很类似， ， ， ， ， ， < / p >
< p > 和数组不同的是， ， （ ） ， ， ： < / p >
< pre > < code class = "language-Go" > func equal(x, y []string) bool {
if len(x) != len(y) {
return false
}
for i := range x {
if x[i] != y[i] {
return false
}
}
return true
}
< / code > < / pre >
< p > 上面关于两个slice的深度相等测试， ， ？ ， ， （ ： ， ） ， < / p >
< p > 第二个原因， ， （ ： ， ） ， ， （ ： ， ） ， ， ， ， ， < / p >
< p > slice唯一合法的比较操作是和nil比较， ： < / p >
< pre > < code class = "language-Go" > if summer == nil { /* ... */ }
< / code > < / pre >
< p > 一个零值的slice等于nil。一个nil值的slice并没有底层数组。一个nil值的slice的长度和容量都是0， ， ， < / p >
< pre > < code class = "language-Go" > var s []int // len(s) == 0, s == nil
s = nil // len(s) == 0, s == nil
s = []int(nil) // len(s) == 0, s == nil
s = []int{} // len(s) == 0, s != nil
< / code > < / pre >
< p > 如果你需要测试一个slice是否是空的， ， ， ； ， < / p >
< p > 内置的make函数创建一个指定元素类型、长度和容量的slice。容量部分可以省略， ， < / p >
< pre > < code class = "language-Go" > make([]T, len)
make([]T, len, cap) // same as make([]T, cap)[:len]
< / code > < / pre >
< p > 在底层， ， ； ， ， ， < / p >
< h3 id = "421-append函数" > < a class = "header" href = "#421-append函数" > 4.2.1. append函数< / a > < / h3 >
< p > 内置的append函数用于向slice追加元素： < / p >
< pre > < code class = "language-Go" > var runes []rune
for _, r := range " Hello, 世界" {
runes = append(runes, r)
}
fmt.Printf(" %q\n" , runes) // " ['H' 'e' 'l' 'l' 'o' ',' ' ' '世' '界']"
< / code > < / pre >
< p > 在循环中使用append函数构建一个由九个rune字符构成的slice， " Hello, 世界" )转换操作完成。< / p >
< p > append函数对于理解slice底层是如何工作的非常重要， ， ： < / p >
< p > < u > < i > gopl.io/ch4/append< / i > < / u > < / p >
< pre > < code class = "language-Go" > func appendInt(x []int, y int) []int {
var z []int
zlen := len(x) + 1
if zlen < = cap(x) {
// There is room to grow. Extend the slice.
z = x[:zlen]
} else {
// There is insufficient space. Allocate a new array.
// Grow by doubling, for amortized linear complexity.
zcap := zlen
if zcap < 2*len(x) {
zcap = 2 * len(x)
}
z = make([]int, zlen, zcap)
copy(z, x) // a built-in function; see text
}
z[len(x)] = y
return z
}
< / code > < / pre >
< p > 每次调用appendInt函数， ， （ ） ， ， ， < / p >
< p > 如果没有足够的增长空间的话， ， ， < / p >
< p > 虽然通过循环复制元素更直接， ， ， < code > dst = src< / code > 赋值语句是一致的。两个slice可以共享同一个底层数组， （ ） ， ， < / p >
< p > 为了提高内存使用效率， ， ： < / p >
< pre > < code class = "language-Go" > func main() {
var x, y []int
for i := 0; i < 10; i++ {
y = appendInt(x, i)
fmt.Printf(" %d cap=%d\t%v\n" , i, cap(y), y)
x = y
}
}
< / code > < / pre >
< p > 每一次容量的变化都会导致重新分配内存和copy操作： < / p >
< pre > < code > 0 cap=1 [0]
1 cap=2 [0 1]
2 cap=4 [0 1 2]
3 cap=4 [0 1 2 3]
4 cap=8 [0 1 2 3 4]
5 cap=8 [0 1 2 3 4 5]
6 cap=8 [0 1 2 3 4 5 6]
7 cap=8 [0 1 2 3 4 5 6 7]
8 cap=16 [0 1 2 3 4 5 6 7 8]
9 cap=16 [0 1 2 3 4 5 6 7 8 9]
< / code > < / pre >
< p > 让我们仔细查看i=3次的迭代。当时x包含了[0 1 2]三个元素， ， ， ， ， < / p >
< p > < img src = "../images/ch4-02.png" alt = "" / > < / p >
< p > 在下一次迭代时i=4， ， ， ， ， ， ； ， ， < / p >
< p > < img src = "../images/ch4-03.png" alt = "" / > < / p >
< p > 内置的append函数可能使用比appendInt更复杂的内存扩展策略。因此， ， ， ， ： < / p >
< pre > < code class = "language-Go" > runes = append(runes, r)
< / code > < / pre >
< p > 更新slice变量不仅对调用append函数是必要的， ， ， ， ， ： < / p >
< pre > < code class = "language-Go" > type IntSlice struct {
ptr *int
len, cap int
}
< / code > < / pre >
< p > 我们的appendInt函数每次只能向slice追加一个元素， ， < / p >
< pre > < code class = "language-Go" > var x []int
x = append(x, 1)
x = append(x, 2, 3)
x = append(x, 4, 5, 6)
x = append(x, x...) // append the slice x
fmt.Println(x) // " [1 2 3 4 5 6 1 2 3 4 5 6]"
< / code > < / pre >
< p > 通过下面的小修改， < / p >
< pre > < code class = "language-Go" > func appendInt(x []int, y ...int) []int {
var z []int
zlen := len(x) + len(y)
// ...expand z to at least zlen...
copy(z[len(x):], y)
return z
}
< / code > < / pre >
< p > 为了避免重复，和前面相同的代码并没有显示。< / p >
< h3 id = "422-slice内存技巧" > < a class = "header" href = "#422-slice内存技巧" > 4.2.2. Slice内存技巧< / a > < / h3 >
< p > 让我们看看更多的例子， ， ： < / p >
< p > < u > < i > gopl.io/ch4/nonempty< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Nonempty is an example of an in-place slice algorithm.
package main
import " fmt"
// nonempty returns a slice holding only the non-empty strings.
// The underlying array is modified during the call.
func nonempty(strings []string) []string {
i := 0
for _, s := range strings {
if s != " " {
strings[i] = s
i++
}
}
return strings[:i]
}
< / code > < / pre >
< p > 比较微妙的地方是， ， ， ： < / p >
< pre > < code class = "language-Go" > data := []string{" one" , " " , " three" }
fmt.Printf(" %q\n" , nonempty(data)) // `[" one" " three" ]`
fmt.Printf(" %q\n" , data) // `[" one" " three" " three" ]`
< / code > < / pre >
< p > 因此我们通常会这样使用nonempty函数： < code > data = nonempty(data)< / code > 。< / p >
< p > nonempty函数也可以使用append函数实现： < / p >
< pre > < code class = "language-Go" > func nonempty2(strings []string) []string {
out := strings[:0] // zero-length slice of original
for _, s := range strings {
if s != " " {
out = append(out, s)
}
}
return out
}
< / code > < / pre >
< p > 无论如何实现， ， ， ， < / p >
< p > 一个slice可以用来模拟一个stack。最初给定的空slice对应一个空的stack， ： < / p >
< pre > < code class = "language-Go" > stack = append(stack, v) // push v
< / code > < / pre >
< p > stack的顶部位置对应slice的最后一个元素： < / p >
< pre > < code class = "language-Go" > top := stack[len(stack)-1] // top of stack
< / code > < / pre >
< p > 通过收缩stack可以弹出栈顶的元素< / p >
< pre > < code class = "language-Go" > stack = stack[:len(stack)-1] // pop
< / code > < / pre >
< p > 要删除slice中间的某个元素并保存原有的元素顺序， ： < / p >
< pre > < code class = "language-Go" > func remove(slice []int, i int) []int {
copy(slice[i:], slice[i+1:])
return slice[:len(slice)-1]
}
func main() {
s := []int{5, 6, 7, 8, 9}
fmt.Println(remove(s, 2)) // " [5 6 8 9]"
}
< / code > < / pre >
< p > 如果删除元素后不用保持原来顺序的话，我们可以简单的用最后一个元素覆盖被删除的元素：< / p >
< pre > < code class = "language-Go" > func remove(slice []int, i int) []int {
slice[i] = slice[len(slice)-1]
return slice[:len(slice)-1]
}
func main() {
s := []int{5, 6, 7, 8, 9}
fmt.Println(remove(s, 2)) // " [5 6 9 8]
}
< / code > < / pre >
< p > < strong > 练习 4.3： < / strong > 重写reverse函数， < / p >
< p > < strong > 练习 4.4： < / strong > 编写一个rotate函数， < / p >
< p > < strong > 练习 4.5： < / strong > 写一个函数在原地完成消除[]string中相邻重复的字符串的操作。< / p >
< p > < strong > 练习 4.6： < / strong > 编写一个函数， （ ） < / p >
< p > < strong > 练习 4.7： < / strong > 修改reverse函数用于原地反转UTF-8编码的[]byte。是否可以不用分配额外的内存？ < / p >
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