Go language slice, range, set

1.Go Language slice (Slice)

summary

Go Language slicing is the abstraction of arrays .

Go The length of the array cannot be changed , In a particular scenario, such a collection is not applicable ,Go Provides a kind of flexibility , Powerful built-in type slicing (“ The dynamic array ”), Compared with array, the length of slice is not fixed , You can append elements , In addition, it may increase the volume of slices .

Defining slices

You can define slices by declaring an array of unspecified size ：

var identifier []type
var si []int

Or use make() Function to create a slice :

var slice1 []type = make([]type, len)

 Or we could just write it as 

slice1 := make([]type, len)

Capacity can also be specified , among capacity Is an optional parameter .

make([]T, length, capacity)

here len Is the length of the array and is also the initial length of the slice .

Slice initialization

s :=[] int {
    1,2,3 }

len() and cap() function

Slices are indexable , And can be len() Method to get the length .

Slicing provides a way to calculate capacity cap() You can measure how long a slice can be .

package main

import "fmt"

func main() {
    
	var numbers = make([]int, 3, 5)
	fmt.Println(len(numbers), cap(numbers), numbers)
}
-----------------------
 Output ：
3 5 [0 0 0]

empty (nil) section

A slice defaults to... Before initialization nil, The length is 0, Examples are as follows ：

package main

import "fmt"

func main() {
    
	var numbers []int
	if numbers == nil {
    
		fmt.Println(" Slice is empty ")
	}
}
--------------------------
 Output ： Slice is empty 

Slice off

package main

import "fmt"

func main() {
    
	numbers := []int{
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
	fmt.Println(numbers)
	fmt.Println(numbers[1:4])
	fmt.Println(numbers[:3])
	fmt.Println(numbers[4:])
}
------------------------------
 Output ：
[0 1 2 3 4 5 6 7 8 9]
[1 2 3]      
[0 1 2]      
[4 5 6 7 8 9]

append() and copy() function

append()

package main

import "fmt"

func main() {
    
	numbers := []int{
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
	/*  Add an element to the slice  */
	numbers = append(numbers, 521)
	/*  Add multiple elements at the same time  */
	numbers = append(numbers, 11, 12, 13)
	fmt.Println(numbers)
}
---------------------------------------------------
 Output ：
[0 1 2 3 4 5 6 7 8 9 521 11 12 13]

copy()

package main

import "fmt"

func main() {
    
	numbers := []int{
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
	/*  Create slices  numbers1  Twice the capacity of the previous slice */
	numbers1 := make([]int, len(numbers), (cap(numbers))*2)
	copy(numbers1, numbers)
	fmt.Println(numbers1)
}
-----------------------------------------------
 Output ：
[0 1 2 3 4 5 6 7 8 9]

---

2.Go Language range (Range)

Go In language range Keywords are used for for Iterating arrays in a loop (array)、 section (slice)、 passageway (channel) Or set (map) The elements of . In the array and slice, it returns the index of the element and the value corresponding to the index , Return... In the collection key-value Yes .

example 1：

package main

import "fmt"

func main() {
    
	//  Use range Ask for one slice And . Using arrays is very similar to this 
	nums := []int{
    2, 3, 4}
	sum := 0
	for _, num := range nums {
    
		sum += num
	}
	fmt.Println(sum)
}
-----------------------------
 Output ：9

example 2：

package main

import "fmt"

func main() {
    
	//  Use range Ask for one slice And . Using arrays is very similar to this 
	nums := []int{
    2, 3, 4}
	sum := 0
	for i, num := range nums {
    
		sum += num
		fmt.Println(i)
	}
	fmt.Println(sum)
}
----------------------------------
 Output ：
0
1
2
9

example 3：range It can also be used to enumerate Unicode character string . The first parameter is the index of the character , The second is the character （Unicode Value ） In itself .

package main

import "fmt"

func main() {
    
	for i, c := range "hello" {
    
		fmt.Println(i, c)
	}
}
---------------------------------------
 Output ：
0 104
1 101
2 108
3 108
4 111

---

3.Go Language Map( aggregate )

Map Is an unordered set of key value pairs .Map The most important point is through key To quickly retrieve data ,key Similar to index , The value that points to the data .

Map It's a collection , So we can iterate it like we iterate arrays and slices . however ,Map Is chaotic , We can't decide the return order , This is because Map It's using hash Table to achieve .

example 1：

package main

import "fmt"

func main() {
    
	var country map[string]string
	country = make(map[string]string)

	/* map Insert key - value Yes  */
	country["France"] = " In Paris, "
	country["beijing"] = " Beijing "
	country["Japan"] = " Japan "

	/*  Use the key to output map values  */
	for cou := range country {
    
		fmt.Println(cou, "+", country[cou])
	}

}
-------------------------------------------------
 Output ：
France +  In Paris, 
beijing +  Beijing 
Japan +  Japan   

example 2：

package main

import "fmt"

func main() {
    
	var country map[string]string
	country = make(map[string]string)

	/* map Insert key - value Yes  */
	country["France"] = " In Paris, "
	country["beijing"] = " Beijing "
	country["Japan"] = " Japan "

	/*  See if the element exists in the collection  */
	capital, ok := country["American"]
	if ok {
    
		fmt.Println(capital)
	} else {
    
		fmt.Println("American There is no capital of ")
	}

}
----------------------------------------
 Output ：
American There is no capital of 

example 3：delete() Function to delete the elements of a collection

package main

import "fmt"

func main() {
    
	var country map[string]string
	country = make(map[string]string)

	/* map Insert key - value Yes  */
	country["France"] = " In Paris, "
	country["beijing"] = " Beijing "
	country["Japan"] = " Japan "

	delete(country, "Japan")
	fmt.Println(country)

}
------------------------------------
 Output ：map[France: In Paris,  beijing: Beijing ]

Copyright notice ： This tutorial is based on the rookie tutorial