Is golang map ordered?

In many programming languages, the map data structure is a very common data structure, which usually consists of keys and values. However, in different programming languages, the implementation and behavior of mapping may be slightly different. In Go, a map is a common data type that is implemented as a hash table and is called a map.

I believe that many developers who are new to the Golang language are quite curious about how Go's map data structure is implemented, whether it is orderly, and whether it is thread-safe. Therefore, this article will give you an in-depth understanding of whether golang map has sequence.

Introduction to Golang Map

In the Golang language, Map is a very useful data type that can be used to store key-value pair data. The implementation of Map is based on a hash table, which means that it can obtain or modify an element in constant time, so it is very fast and efficient.

Here is an example of using a Map to store email addresses:

emailMap := map[string]string{
    "john@example.com": "John",
    "jane@example.com": "Jane",
    "bob@example.com":  "Bob",
}

In the above example, we used a Map object to store email addresses and corresponding usernames. We can get the value (value) through the key (key), as shown below:

fmt.Println(emailMap["john@example.com"]) // Output: John

As you can see, we obtained the corresponding value John through emailMap["john@example.com"].

Traversal of Golang Map

In Golang, we can use the range keyword to traverse a Map. The sample code is as follows:

for k, v := range emailMap {
    fmt.Printf("%s: %s
", k, v)
}

In the above code, k represents the key , v represents values, and we can use them as needed to perform corresponding operations.

Is Golang Map ordered?

After testing and actual use, Golang Map is unordered, which means you cannot guarantee the order of the elements stored in the Map. In other words, if you add elements to a Map in a specific order, it does not mean that they will be stored in the same order or traversed in the same order.

To demonstrate this, we can use the following sample code:

emailMap := map[string]string{
    "john@example.com": "John",
    "jane@example.com": "Jane",
    "bob@example.com":  "Bob",
}

for k, v := range emailMap {
    fmt.Printf("%s: %s
", k, v)
}

If we run this code multiple times, we will find that the order of the output elements is random.

The reason for this unordered characteristic is that the implementation of Golang Map is a hash table. A hash table is an extension of a hash table. It uses a hash function to map keys to specific positions in the array. superior. When the map items are stored into an array using a hash function, they are not sorted in their order.

Methods to solve the disorder of Golang Map

Although Golang Map is disordered, if we need an ordered Map, we can achieve it through some hacks.

Method 1: Use structure sorting

You can convert the key/value pairs in the Map into structure slices, then use the function of the sort package to sort the structure slices, and finally convert them back to Map. The sample code is as follows:

type kv struct {
    Key   string
    Value string
}

var ss []kv
for k, v := range emailMap {
    ss = append(ss, kv{k, v})
}

sort.Slice(ss, func(i, j int) bool {
    return ss[i].Key > ss[j].Key
})

for _, kv := range ss {
    fmt.Printf("%s: %s
", kv.Key, kv.Value)
}

In the above code, we first define a structure named kv, which includes two fields, Key and Value. Then we defined a kv slice named ss and converted the key-value pairs in the Map into structures in the slice. Next, we sorted the slices by calling the sort.Slice function, and finally used a loop to output the slices. Key-value pairs.

Method 2: Use the ordered map library

For the convenience of developers, there are many third-party libraries that can implement ordered maps, such as go-ordered-map and orderedmap. Using these libraries, you can easily implement ordered maps without using the hack mentioned above.

Thread safety of Golang Map

When multiple goroutines access Map concurrently, the data of Map may be damaged or lost. Therefore, when using Map in Golang, you need to pay attention to its thread safety.

In order to solve this problem, Golang provides the sync package, in which the Mutex and RWMutex types can be used to control goroutine access. The following is an example of using Mutex to implement Map thread safety:

type SafeMap struct {
    mu sync.Mutex
    m  map[string]string
}

func (sm *SafeMap) Get(key string) (string, bool) {
    sm.mu.Lock()
    defer sm.mu.Unlock()

    v, ok := sm.m[key]
    return v, ok
}

func (sm *SafeMap) Set(key, value string) {
    sm.mu.Lock()
    defer sm.mu.Unlock()

    sm.m[key] = value
}

In the above code, we define a structure named SafeMap, which contains a Mutex and a Map. The Get function uses Mutex to control access to the Map. The Set function also locks the Map and then performs related operations before unlocking it.

Summary

Map in Golang is a very common and practical data type, which allows us to easily store and access key-value pair data. Although Golang Map is unordered, ordered Map can be achieved by using some tricks. At the same time, when multiple goroutines operate Map, they need to pay attention to their thread safety, which can be achieved using Mutex and RWMutex of the sync package.

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