Why are keys unordered in golang map

Golang Map Medium key Why is it out of order

Golang Easy to learn

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One 、 Why is it out of order ？

Come to the point , First on the source code

func mapiterinit(t *maptype, h *hmap, it *hiter) {
    
 
	// decide where to start
	r := uintptr(fastrand())
	if h.B > 31-bucketCntBits {
    
		r += uintptr(fastrand()) << 31
	}
	
	mapiternext(it)
}

Go When we're traversing map when , It is not fixed to traverse from the first number , Each time, it starts from one position . Even one that will not change map, Just traverse it , It is also unlikely to return to a fixed order .
in other words ,GO Language proceeds from language Map Disorder of .

Two 、GO Why do you do this ？

In fact, it is mainly because of map After the expansion , There may be some key Move to new memory , Then this part is actually out of order . And the traversal process , In fact, it is to traverse memory addresses in order , At the same time, the memory addresses are traversed in order key. But it was already out of order .

Of course someone would say , If I were just one map, I promise not to map Perform operations such as modification and deletion , It is reasonable to say that there will be no change without capacity expansion . But also because of this ,GO In the source code
Add random elements , Traversal map Order randomization of , It is used to prevent users from traversing in sequence . And this is risky code , stay GO Under the strict grammatical rules of , It is strongly discouraged .

3、 ... and 、 Whether traversal is really disordered

1. First traversal

The code is as follows （ Example ）：

package main

import "fmt"

func main() {
    

	noSortMap := map[int]int{
    
		1: 1,
		2: 2,
		3: 3,
		4: 4,
		5: 5,
		6: 6,
	}

	for k, v := range noSortMap {
    

		fmt.Println("key: ", k, "value: ", v)
	}

}

It turned out just as expected , It doesn't start with the first number

2. Second traversal

Same code as above ：

It turned out just as expected , Different from the first time

Four 、 How to get ordered key value pairs

We need to use section （Slice) To control ,

1. Detailed code

The code is as follows （ Example ）：

package main

import (
	"fmt"
	"sort"
)

func main() {
    

	noSortMap := map[int]int{
    
		1: 1,
		2: 2,
		3: 3,
		4: 4,
		5: 5,
		6: 6,
	}

	var noSortSlice []int
	for k, v := range noSortMap {
    

		noSortSlice = append(noSortSlice, k)
		fmt.Println("key: ", k, "value: ", v)
	}

	fmt.Println(noSortSlice)
	//  Sort 
	sort.Ints(noSortSlice)
	sortSlice := noSortSlice
	fmt.Println(sortSlice)
	for _, k := range sortSlice {
    

		fmt.Println("key: ", k, "value: ", noSortMap[k])
	}
	
}

First, the disordered key Put it in the slice

Then slice the disordered slices call sort Bag Ints Methods the sorting

After sorting, traverse the slice , The slices are now in order , be map The key value pairs of are also ordered

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summary

Don't rely on map Traversal returns key The order , By randomly selecting the starting position of traversal, the return is out of order . If you want to get ordered key values , Please rely on ordered slices for access to get an effective order Map

I hope this blog will be beneficial to you . I am the light king , I represent myself. .