What is map in Go language?

Go language is an open source programming language. It is a system-level programming language developed by Google and is widely used in high-performance and large-scale projects. Among them, map in Go language is a very important data type, which is widely used in various types of development. This article will introduce what map is in Go language and how to use it.

1. What is map

In the Go language, map is a data structure similar to a hash table. A map is unordered and consists of a set of key-value pairs, with each key appearing only once. The keys in the map must be data types that support equality comparison, such as strings, numbers, bool, etc. The value can be any type of data, such as strings, numbers, structures, slices, etc.

The declaration of map in Go language requires the use of the make function, as shown below:

var mapName = make(map[keyType]valueType)

Among them, mapName is the variable name of the map, keyType is the type of the key, and valueType is the type of the value. For example, we can declare a map with a key type of string and a value type of int, as shown below:

var myMap = make(map[string]int)

2. Map operations

1. Add elements

To add elements to the map, you need to use the assignment symbol for assignment, as shown below:

myMap["one"] = 1
myMap["two"] = 2

In the above example, we added two key-value pairs to myMap, where the key is "one " and "two", the corresponding values ​​are 1 and 2.

2. Get elements

To get elements in the map, you can use the subscript operator [], as shown below:

value := myMap["one"]

In the above example , we use the subscript operator [] to obtain the value with the key "one" in myMap and save it in the variable value.

It should be noted that if the key does not exist in the map, the zero value corresponding to the value type will be returned. For example, if we get a key that does not exist as follows:

value := myMap["three"]

Then the value of the variable value will be the zero value 0 of type int.

3. Modify elements

To modify elements in the map, you can directly use the subscript operator [] to assign values, as shown below:

myMap["one"] = 100

In the above example, we change the value of the key "one" in myMap to 100.

4. Delete elements

To delete elements from the map, you can use the delete function in the Go language, as shown below:

delete(myMap, "one")

In the above example , we removed the element with key "one" from myMap.

5. Get the length of the map

To get the length of the map, you can use the len function in the Go language, as shown below:

length := len(myMap)

In the above example , we get the length of myMap and save it in the variable length.

3. Traverse the map

There are many ways to traverse the map, the most commonly used method is to use a for loop, as shown below:

for key, value := range myMap {
    fmt.Println(key, value)
}

In the above example, We iterate through all key-value pairs in myMap and output them to the console.

It should be noted that the map is unordered during traversal, and the order of key-value pairs returned each time it is traversed is random.

4. Features of map

1. Thread safety

By default, map is not thread-safe. If multiple threads modify the same map at the same time, data competition and data inconsistency will occur. In order to solve this problem, the Go language provides the sync package, in which the sync.Map type can implement a thread-safe map.

2. Does not support comparison operators

The key type of map must support equality comparison operators, such as strings, numbers, bool, etc., but slicing in Go language , structures and other types do not support equality comparison operators. If you want to use these types as keys in a map, you can use pointers or write a custom comparison function.

3. Dynamic Scaling

The underlying implementation of map is a hash table. When the elements in the map increase or decrease, the underlying hash table will also dynamically expand and contract. This process allocates more memory and recalculates the hash value. Therefore, the performance of map operations will be affected when processing large amounts of data.

Conclusion

In this article, we introduced map in the Go language, which is a very important data type and is widely used in various types of development. We learned what a map is, how to operate a map, and its properties. I hope that through the introduction of this article, readers can have an in-depth understanding of maps in the Go language and help develop more efficient and stable applications.

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