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Merge pull request #25836 from lkxed/20180712-An-introduction-to-Go-arrays-and-slices
[提交译文][tech]: 20180712 An introduction to Go arrays and slices.md
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[#]: subject: "An introduction to Go arrays and slices"
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[#]: via: "https://opensource.com/article/18/7/introduction-go-arrays-and-slices"
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[#]: author: "Mihalis Tsoukalos https://opensource.com/users/mtsouk"
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[#]: collector: "lkxed"
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[#]: translator: "lkxed"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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An introduction to Go arrays and slices
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======
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Learn the pros and cons of storing data in Go using arrays and slices and why one is usually better than the other.
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![Testing certificate chains with a 34-line Go program][1]
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Image by: carrotmadman6. Modified by Opensource.com. CC BY-SA 2.0
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In this fourth article in the series, I will explain [Go][5] arrays and slices, how to use them, and why you'll usually want to choose one over the other.
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### Arrays
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Arrays are one of the most popular data structures among programming languages for two main reasons: They are simple and easy to understand, and they can store many different kinds of data.
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You can declare a Go array named `anArray` that stores four integers with the following:
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```
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anArray := [4]int{-1, 2, 0, -4}
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```
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The array's size should be stated before its type, which should be defined before its elements. The `len()` function can help you find the length of any array. The size of the array above is 4.
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If you are familiar with other programming languages, you might try to access all the elements of an array using a `for` loop. However, as you will see below, Go's `range` keyword allows you to access all the elements of an array or a slice in a more elegant way.
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Last, here is how you can define an array with two dimensions:
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```
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twoD := [3][3]int{
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{1, 2, 3},
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{6, 7, 8},
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{10, 11, 12}}
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```
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The `arrays.go` source file explains the use of Go arrays. The most important code in `arrays.go` is:
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```
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for i := 0; i < len(twoD); i++ {
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k := twoD[i]
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for j := 0; j < len(k); j++ {
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fmt.Print(k[j], " ")
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}
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fmt.Println()
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}
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for _, a := range twoD {
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for _, j := range a {
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fmt.Print(j, " ")
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}
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fmt.Println()
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}
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```
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This shows how you can iterate over the elements of an array using a `for` loop and the `range` keyword. The rest of the code of `arrays.go` shows how to pass an array into a function as a parameter.
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Following is the output of `arrays.go` :
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```
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$ go run arrays.go
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Before change(): [-1 2 0 -4]
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After change(): [-1 2 0 -4]
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1 2 3
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6 7 8
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10 11 12
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1 2 3
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6 7 8
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10 11 12
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```
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This output demonstrates that the changes you make to an array inside a function are lost after the function exits.
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### Disadvantages of arrays
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Go arrays have many disadvantages that will make you reconsider using them in your Go projects. First, you can't change the size of an array after you define it, which means Go arrays are not dynamic. Putting it simply, if you need to add an element to an array that doesn't have any space left, you will need to create a bigger array and copy all the elements of the old array to the new one. Second, when you pass an array to a function as a parameter, you actually pass a copy of the array, which means any changes you make to an array inside a function will be lost after the function exits. Last, passing a large array to a function can be pretty slow, mostly because Go has to create a copy of the array.
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The solution to all these problems is to use Go slices.
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### Slices
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A Go slice is similar to a Go array without the shortcomings. First, you can add an element to an existing slice using the `append()` function. Moreover, Go slices are implemented internally using arrays, which means Go uses an underlying array for each slice.
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Slices have a *capacity* property and a *length* property, which are not always the same. The length of a slice is the same as the length of an array with the same number of elements, and it can be found using the `len()` function. The capacity of a slice is the room that has currently been allocated for the slice, and it can be found with the `cap()` function.
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As slices are dynamic in size, if a slice runs out of room (which means the current length of the array is the same as its capacity while you are trying to add another element to the array), Go automatically doubles its current capacity to make room for more elements and adds the requested element to the array.
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Additionally, slices are passed by reference to functions, which means what is actually passed to a function is the memory address of the slice variable, and any modifications you make to a slice inside a function won't get lost after the function exits. As a result, passing a big slice to a function is significantly faster than passing an array with the same number of elements to the same function. This is because Go will not have to make a copy of the slice—it will just pass the memory address of the slice variable.
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Go slices are illustrated in `slice.go`, which contains the following code:
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```
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package main
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import (
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"fmt"
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)
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func negative(x []int) {
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for i, k := range x {
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x[i] = -k
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}
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}
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func printSlice(x []int) {
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for _, number := range x {
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fmt.Printf("%d ", number)
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}
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fmt.Println()
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}
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func main() {
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s := []int{0, 14, 5, 0, 7, 19}
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printSlice(s)
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negative(s)
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printSlice(s)
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fmt.Printf("Before. Cap: %d, length: %d\n", cap(s), len(s))
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s = append(s, -100)
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fmt.Printf("After. Cap: %d, length: %d\n", cap(s), len(s))
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printSlice(s)
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anotherSlice := make([]int, 4)
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fmt.Printf("A new slice with 4 elements: ")
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printSlice(anotherSlice)
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}
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```
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The biggest difference between a slice definition and an array definition is that you do not need to specify the size of the slice, which is determined by the number of elements you want to put in it. Additionally, the `append()` function allows you to add an element to an existing slice—notice that even if the capacity of a slice allows you to add an element to that slice, its length will not be modified unless you call `append()`. The `printSlice()` function is a helper function used for printing the elements of its slice parameter, whereas the `negative()` function processes all the elements of its slice parameter.
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The output of `slice.go` is:
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```
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$ go run slice.go
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0 14 5 0 7 19
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0 -14 -5 0 -7 -19
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Before. Cap: 6, length: 6
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After. Cap: 12, length: 7
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0 -14 -5 0 -7 -19 -100
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A new slice with 4 elements: 0 0 0 0
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```
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Please note that when you create a new slice and allocate memory space for a given number of elements, Go will automatically initialize all the elements to the zero value of its type, which in this case is 0.
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### Referencing arrays with slices
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Go allows you to reference an existing array with a slice using the `[:]` notation. In that case, any changes you make into a slice's function will be propagated to the array—this is illustrated in `refArray.go`. Please remember that the `[:]` notation does not create a copy of the array, just a reference to it.
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The most interesting part of `refArray.go` is:
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```
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func main() {
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anArray := [5]int{-1, 2, -3, 4, -5}
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refAnArray := anArray[:]
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fmt.Println("Array:", anArray)
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printSlice(refAnArray)
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negative(refAnArray)
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fmt.Println("Array:", anArray)
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}
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```
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The output of `refArray.go` is:
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```
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$ go run refArray.go
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Array: [-1 2 -3 4 -5]
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-1 2 -3 4 -5
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Array: [1 -2 3 -4 5]
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```
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So, the elements of the `anArray` array changed because of the slice reference to it.
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### Summary
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Although Go supports both arrays and slices, it should be clear by now that you will most likely use slices because they are more versatile and powerful than Go arrays. There are only a few occasions where you will need to use an array instead of a slice. The most obvious one is when you are absolutely sure that you will need to store a fixed number of elements.
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You can find the Go code of `arrays.go`, `slice.go`, and `refArray.go` at [GitHub][6].
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If you have any questions or feedback, please leave a comment below or reach out to me on [Twitter][7].
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/18/7/introduction-go-arrays-and-slices
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作者：[Mihalis Tsoukalos][a]
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选题：[lkxed][b]
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译者：[译者ID](https://github.com/译者ID)
|
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校对：[校对者ID](https://github.com/校对者ID)
|
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|
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
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|
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[a]: https://opensource.com/users/mtsouk
|
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[b]: https://github.com/lkxed
|
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[1]: https://opensource.com/sites/default/files/lead-images/traffic-light-go.png
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[2]: https://opensource.com/article/18/5/creating-random-secure-passwords-go
|
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[3]: https://opensource.com/article/18/5/building-concurrent-tcp-server-go
|
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[4]: https://opensource.com/article/18/6/copying-files-go
|
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[5]: https://golang.org/
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[6]: https://github.com/mactsouk/opensource.com
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[7]: https://twitter.com/mactsouk
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@ -0,0 +1,216 @@
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[#]: subject: "An introduction to Go arrays and slices"
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[#]: via: "https://opensource.com/article/18/7/introduction-go-arrays-and-slices"
|
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[#]: author: "Mihalis Tsoukalos https://opensource.com/users/mtsouk"
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[#]: collector: "lkxed"
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[#]: translator: "lkxed"
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[#]: reviewer: " "
|
||||
[#]: publisher: " "
|
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[#]: url: " "
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Go 数组和切片的介绍
|
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======
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了解使用数组和切片在 Go 中存储数据的优缺点，以及为什么其中一个比另一个更好。
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![][1]
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图源：carrotmadman6，经 Opensource.com 修改，CC BY-SA 2.0
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|
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在本系列的第四篇文章中，我将解释 [Go][5] 数组和切片，包括如何使用它们，以及为什么你通常要选择其中一个而不是另一个。
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### 数组
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数组是编程语言中最流行的数据结构之一，主要原因有两个：一是简单易懂，二是可以存储许多不同类型的数据。
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|
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你可以声明一个名为 `anArray` 的 Go 数组，该数组存储四个整数，如下所示：
|
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|
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```
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anArray := [4]int{-1, 2, 0, -4}
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```
|
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数组的大小应该在它的类型之前声明，而类型应该在声明元素之前定义。`len()` 函数可以帮助你得到任何数组的长度。上面数组的大小是 4。
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如果你熟悉其他编程语言，你可能会尝试使用 `for` 循环来遍历数组。Go 当然也支持 `for` 循环，不过，正如你将在下面看到的，Go 的 `range` 关键字可以让你更优雅地遍历数组或切片。
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最后，你也可以定义一个二维数组，如下：
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```
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twoD := [3][3]int{
|
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{1, 2, 3},
|
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{6, 7, 8},
|
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{10, 11, 12}}
|
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```
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|
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The `arrays.go` source file explains the use of Go arrays. The most important code in `arrays.go` is:
|
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`arrays.go` 源文件中包含了 Go 数组的示例代码。其中最重要的部分是：
|
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|
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```
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for i := 0; i < len(twoD); i++ {
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k := twoD[i]
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for j := 0; j < len(k); j++ {
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fmt.Print(k[j], " ")
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}
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fmt.Println()
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||||
}
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|
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for _, a := range twoD {
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for _, j := range a {
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fmt.Print(j, " ")
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}
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fmt.Println()
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}
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```
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通过上述代码，我们知道了如何使用 `for` 循环和 `range` 关键字迭代数组的元素。`arrays.go` 的其余代码则展示了如何将数组作为参数传递给函数。
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以下是 `arrays.go` 的输出：
|
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|
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```
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$ go run arrays.go
|
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Before change(): [-1 2 0 -4]
|
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After change(): [-1 2 0 -4]
|
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1 2 3
|
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6 7 8
|
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10 11 12
|
||||
1 2 3
|
||||
6 7 8
|
||||
10 11 12
|
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```
|
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|
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这个输出告诉我们：对函数内的数组所做的更改，会在函数退出后丢失。
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### 数组的缺点
|
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|
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Go 数组有很多缺点，你应该重新考虑是否要在 Go 项目中使用它们。
|
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|
||||
首先，数组定义之后，大小就无法改变，这意味着 Go 数组不是动态的。简而言之，如果你需要将一个元素添加到一个没有剩余空间的数组中，你将需要创建一个更大的数组，并将旧数组的所有元素复制到新数组中。
|
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|
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其次，当你将数组作为参数传递给函数时，实际上是传递了数组的副本，这意味着你对函数内部的数组所做的任何更改，都将在函数退出后丢失。
|
||||
|
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最后，将大数组传递给函数可能会很慢，主要是因为 Go 必须创建数组的副本。
|
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|
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以上这些问题的解决方案，就是使用 Go 切片。
|
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|
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### 切片
|
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|
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Go 切片与 Go 数组类似，但是它没有后者的缺点。
|
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|
||||
首先，你可以使用 `append()` 函数将元素添加到现有切片中。此外，Go 切片在内部使用数组实现，这意味着 Go 中每个切片都有一个底层数组。
|
||||
|
||||
切片具有 `capacity` 属性和 `length` 属性，它们并不总是相同的。切片的长度与元素个数相同的数组的长度相同，可以使用 `len()` 函数得到。切片的容量是当前为切片分配的空间，可以使用 `cap()` 函数得到。
|
||||
|
||||
由于切片的大小是动态的，如果切片空间不足（也就是说，当你尝试再向切片中添加一个元素时，底层数组的长度恰好与容量相等），Go 会自动将它的当前容量加倍，使其空间能够容纳更多元素，然后将请求的元素添加到底层数组中。
|
||||
|
||||
此外，切片是通过引用传递给函数的，这意味着实际传递给函数的是切片变量的内存地址，这样一来，你对函数内部的切片所做的任何修改，都不会在函数退出后丢失。因此，将大切片传递给函数，要比将具有相同数量元素的数组传递给同一函数快得多。这是因为 Go 不必拷贝切片 —— 它只需传递切片变量的内存地址。
|
||||
|
||||
Go slices are illustrated in `slice.go`, which contains the following code:
|
||||
`slice.go` 源文件中有 Go 切片的代码示例，其中包含以下代码：
|
||||
|
||||
```
|
||||
package main
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
)
|
||||
|
||||
func negative(x []int) {
|
||||
for i, k := range x {
|
||||
x[i] = -k
|
||||
}
|
||||
}
|
||||
|
||||
func printSlice(x []int) {
|
||||
for _, number := range x {
|
||||
fmt.Printf("%d ", number)
|
||||
}
|
||||
fmt.Println()
|
||||
}
|
||||
|
||||
func main() {
|
||||
s := []int{0, 14, 5, 0, 7, 19}
|
||||
printSlice(s)
|
||||
negative(s)
|
||||
printSlice(s)
|
||||
|
||||
fmt.Printf("Before. Cap: %d, length: %d\n", cap(s), len(s))
|
||||
s = append(s, -100)
|
||||
fmt.Printf("After. Cap: %d, length: %d\n", cap(s), len(s))
|
||||
printSlice(s)
|
||||
|
||||
anotherSlice := make([]int, 4)
|
||||
fmt.Printf("A new slice with 4 elements: ")
|
||||
printSlice(anotherSlice)
|
||||
}
|
||||
```
|
||||
|
||||
切片和数组在定义方式上的最大区别就在于：你不需要指定切片的大小。实际上，切片的大小取决于你要放入其中的元素数量。此外，`append()` 函数允许你将元素添加到现有切片 —— 请注意，即使切片的容量允许你将元素添加到该切片，它的长度也不会被修改，除非你调用 `append ()`。上述代码中的 `printSlice()` 函数是一个辅助函数，用于打印切片中的所有元素，而 `negative()` 函数将切片中的每个元素都变为各自的相反数。
|
||||
|
||||
运行 `slice.go` 将得到以下输出：
|
||||
|
||||
```
|
||||
$ go run slice.go
|
||||
0 14 5 0 7 19
|
||||
0 -14 -5 0 -7 -19
|
||||
Before. Cap: 6, length: 6
|
||||
After. Cap: 12, length: 7
|
||||
0 -14 -5 0 -7 -19 -100
|
||||
A new slice with 4 elements: 0 0 0 0
|
||||
```
|
||||
|
||||
请注意，当你创建一个新切片，并为给定数量的元素分配内存空间时，Go 会自动地将所有元素都初始化为其类型的零值，在本例中为 0（`int` 类型的零值）。
|
||||
|
||||
### 使用切片来引用数组
|
||||
|
||||
Go 允许你使用 `[:]` 语法，使用切片来引用现有的数组。在这种情况下，你对切片所做的任何更改都将传播到数组中 —— 详见 `refArray.go`。请记住，使用 `[:]` 不会创建数组的副本，它只是对数组的引用。
|
||||
|
||||
`refArray.go` 中最有趣的部分是：
|
||||
|
||||
```
|
||||
func main() {
|
||||
anArray := [5]int{-1, 2, -3, 4, -5}
|
||||
refAnArray := anArray[:]
|
||||
|
||||
fmt.Println("Array:", anArray)
|
||||
printSlice(refAnArray)
|
||||
negative(refAnArray)
|
||||
fmt.Println("Array:", anArray)
|
||||
}
|
||||
```
|
||||
|
||||
运行 `refArray.go`，输出如下：
|
||||
|
||||
```
|
||||
$ go run refArray.go
|
||||
Array: [-1 2 -3 4 -5]
|
||||
-1 2 -3 4 -5
|
||||
Array: [1 -2 3 -4 5]
|
||||
```
|
||||
|
||||
我们可以发现：对 `anArray` 数组的切片引用进行了操作后，它本身也被改变了。
|
||||
|
||||
### 总结
|
||||
|
||||
尽管 Go 提供了数组和切片两种类型，你很可能还是会使用切片，因为它们比 Go 数组更加通用、强大。只有少数情况需要使用数组而不是切片，特别是当你完全确定元素的数量固定不变时。
|
||||
|
||||
你可以在 [GitHub][6] 上找到 `arrays.go`、`slice.go` 和 `refArray.go` 的源代码。
|
||||
|
||||
如果您有任何问题或反馈，请在下方发表评论或在 [Twitter][7] 上与我联系。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/18/7/introduction-go-arrays-and-slices
|
||||
|
||||
作者：[Mihalis Tsoukalos][a]
|
||||
选题：[lkxed][b]
|
||||
译者：[lkxed](https://github.com/lkxed)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/mtsouk
|
||||
[b]: https://github.com/lkxed
|
||||
[1]: https://opensource.com/sites/default/files/lead-images/traffic-light-go.png
|
||||
[2]: https://opensource.com/article/18/5/creating-random-secure-passwords-go
|
||||
[3]: https://opensource.com/article/18/5/building-concurrent-tcp-server-go
|
||||
[4]: https://opensource.com/article/18/6/copying-files-go
|
||||
[5]: https://golang.org/
|
||||
[6]: https://github.com/mactsouk/opensource.com
|
||||
[7]: https://twitter.com/mactsouk
|
||||
Loading…
Reference in New Issue
Block a user