[Go Affair] See through Go's collections and slices at a glance

️ Go 集合

在 Go The keywords associated with collections in are Map,It represents an unnecessary collection of key-value pairs,Map 可以通过 Key 检索值,这一点和 Python The dictionary in is especially similar.

集合是无序的,并且使用 hash 表实现.

定义集合

使用 map Keywords define collections,原型如下：

var map_name map[key_type]value_type

参数说明如下：

• map_name：集合变量名;
• key_type：键类型;
• value_type：值类型.

Go 中的 map 可动态扩展,There is no need to declare the length like an array.

Next, make a simple declaration and use,代码如下：

package main

import (
	"fmt"
)

func main() {
    
	// 创建集合
	var map_var map[string]string

	// 在使用 map 前,需要先 make,Its role is to give map 分配数据空间
	map_var = make(map[string]string)
	map_var["red"] = "红色"
	map_var["green"] = "绿色"
	map_var["blue"] = "蓝色"

	for color := range map_var {
    
		fmt.Println(color, "中文：", map_var[color])
	}
}

Be careful if you create a collection,但是没有使用 make 函数,就会报错,The reason is also unallocated memory.

Do not use if desired map You can declare and initialize collections,可以在声明的时候,直接赋值.

package main

import (
	"fmt"
)

func main() {
    
	// 创建集合
	map_var := map[string]string{
    
		"red":   "红色",
		"green": "绿色",
		"blue":  "蓝色",
	}

	for color := range map_var {
    
		fmt.Println(color, "中文：", map_var[color])
	}
}

Map 元素删除

直接使用内置的 delete 方法即可.

package main

import (
	"fmt"
)

func main() {
    
	// 创建集合
	map_var := map[string]string{
    
		"red":   "红色",
		"green": "绿色",
		"blue":  "蓝色",
	}
	// 删除一个元素
	delete(map_var, "red")
	for color := range map_var {
    
		fmt.Println(color, "中文：", map_var[color])
	}
}

Go 切片

在 Python Mentioned in slicing is only taking a subset of the list,但是在 Go is an abstraction of an array,在 Go Medium slices are one type,Also called dynamic array,Expansion elements can be added.

A slice structure consists of three parts,Pointer 指向数组的指针,len 切片的长度,cap 切片容量,容量大于等于长度.

We can declare directly【size not set】An array of defined slices,The basic syntax format is ：

var identifier []type

The above statement defaults to nil,其中 len=0,cap=0.

Use the following code to test.

package main

import "fmt"

func main() {
    
	var slice_var []int

	sliceFormat(slice_var)

	if slice_var == nil {
    
		fmt.Printf("空切片")
	}
}

func sliceFormat(x []int) {
    
	fmt.Printf("len=%d cap=%d slice=%v\n", len(x), cap(x), x)
}

Declare a slice with an initial length or a specific capacity,使用 make 函数完成.

var slice_var []type = make([]type, length, capacity)

where the first parameter is the type,第二个是切片的长度,在这种情况下,So is the capacity of the slice 5,The following code can be tested.

capacity 可以缺省,即下述代码：

package main

import "fmt"

func main() {
    
	num_slice := make([]int, 5)
	printSlice(num_slice)
}

func printSlice(x []int) {
    
	fmt.Printf("len=%d cap=%d slice=%v\n", len(x), cap(x), x)
}

运行代码,得到下述输出：

len=5 cap=5 slice=[0 0 0 0 0]

You can test switching different types,例如 bool,Slices are automatically initialized by the system as false.

len=5 cap=5 slice=[false false false false false]

Initialize the slice while declaring it

package main

import "fmt"

func main() {
    
	slice_var := []int{
    1, 2, 3}
	printSlice(slice_var)
}

func printSlice(x []int) {
    
	fmt.Printf("len=%d cap=%d slice=%v\n", len(x), cap(x), x)
}

The above code directly completes the slice declaration and initialization operations,Indicates slice usage [] 符号,{1,2,3} Indicates initialization data.

Elements can be added to already declared slices,需要使用内建函数 append 添加元素.

package main

import "fmt"

func main() {
    
	num_slice := make([]int, 5, 10)
	num_slice = append(num_slice, 6)
	printSlice(num_slice)
}

func printSlice(x []int) {
    
	fmt.Printf("len=%d cap=%d slice=%v\n", len(x), cap(x), x)
}

After multiple verifications,will be found when the length is greater than 2 时,The capacity of the slice will be automatically expanded to the original one 2 倍.

# 当 len =10 ,cap =10 时,输出结果
len=10 cap=10 slice=[0 0 0 0 0 6 7 8 9 10]
# The result after expansion
len=11 cap=20 slice=[0 0 0 0 0 6 7 8 9 10 11]

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