[golang learning notes 2.0] arrays and slices in golang

Introduction of the array

1. Arrays can hold multiple Same type of data , Arrays are also a data type , stay go The array in is a value type .
2. Definition of array ： var Array name [ Array size ] data type

go Precautions for the use of arrays in

1. An array is a combination of multiple data of the same type , Once the array is defined , Its length is fixed , Can't change dynamically .
2. The elements in the array can be of any data type , Including value types and reference types , But don't mix .
3. After the array is created If there is no assignment . Arrays have default values .int Default 0 string Default empty string "",bool type Default false
4. The subscript of the array is 0 Start with 【 Basically, arrays in most languages are subscripts 0 Start with 】
5. go The array is a value type , By default, the value will be copied blindly . Arrays will not affect
6. If you want to use it in other functions , To modify the original array . You can use reference passing .

Introduction to slicing

1. Slice array get a reference , Therefore, the type of slice is reference type , So when it's worth passing , Follow the reference passing mechanism .
2. Slicing is similar to array . The length of the slice can be changed . So slice can be understood as defining an empty array 【 Be similar to php in $arr=array()】
3. Basic syntax for slice definition var Variable name [] type ; example ：var arr [] int
4. The slice is equivalent to a structure from the bottom ;

type slice struct{
    
   ptr *[2]int
   len int 
   cap int 
 }

Several ways to declare slices

1. The first one is ： Declare an array of unspecified size to define the slice

package main
import (
	"fmt"
)
func main() {
    
	// Declare an array of unspecified size to define the slice 
	var slice []int
	// It is impossible to assign values directly like this , An error will be reported that the index is out of range 
	// slice[0] =4
	// This situation requires append Function to append data 
	slice = append(slice, 1)
	slice = append(slice, 2)
	slice = append(slice, 3)
	// You can re assign values within the existing index range in this way ,slice[3]=5  This is not going to work .
	slice[2] =4
	// Print the results  slice: [1 2 4]
	fmt.Printf("slice: %v\n", slice)
}

2. The second kind ： Use make Function to declare a slice

package main
import (
	"fmt"
)
func main() {
    
	// Declare an array of unspecified size to define the slice 
	//make( Type of slice , The length of the slice , The volume of the slice )
	var slice []int=make([]int, 10,20)
	// Print the results ：slice: [0 0 0 0 0 0 0 0 0 0]
	fmt.Printf("slice: %v\n", slice)
}

3. The third kind of ： Use make Function to declare a slice

package main
import (
	"fmt"
)
func main() {
    
	// Assign values directly ; Be similar to make
	var slice []int=[]int{
    1,2,3}
	// Print the results ：slice: [1 2 3]
	fmt.Printf("slice: %T\n", slice)
}

4. A fourth ： Create slices by referencing arrays

package main
import (
	"fmt"
)
func main() {
    
	// The form of a reference array 
	var arr [6]int = [...]int{
    1, 2, 3, 4, 5, 6}
	slice := arr[1:4]
	// Print the results ：slice: [2 3 4]
	fmt.Printf("slice: %v\n", slice)
}