How to solve 'assignment to entry in nil map' error in golang?

In the process of using golang for development, we often encounter the "assignment to entry in nil map" error. This error often occurs when we try to insert key-value pairs into a nil map. In this article, we will learn how to avoid this mistake.

To better understand this error, we first need to understand what map is. In golang, map is a data structure that stores key-value pairs. Through map, we can easily operate on key-value pairs, such as adding, modifying, deleting, etc.

When we first start using map, sometimes the following code snippet will appear:

var m map[string]int
m["one"] = 1

In this code, we first declare a map named m, and then try to change the key The value pair "one:1" is added to the map. However, running this code will get the following error message:

panic: assignment to entry in nil map

This error indicates that we are trying to add a key-value pair to a nil map, which is not allowed. So, how to avoid this mistake?

First, we can initialize a map through the make function, as shown below:

m := make(map[string]int)
m["one"] = 1

In this sample code, we use the make function to initialize a map, and then we can add it to it Add the key value right. Doing this will avoid “assignment to entry in nil map” errors.

In addition, when we need to add key-value pairs to an existing map, we need to first check whether the map is empty. If it is empty, we need to initialize it first and then operate it. The sample code is as follows:

var m map[string]int
if m == nil {
    m = make(map[string]int)
}
m["one"] = 1

Finally, we can also use sync.Map to avoid this error. sync.Map is a thread-safe map implementation provided in the golang standard library. It can automatically handle nil map situations, thereby avoiding "assignment to entry in nil map" errors. The sample code is as follows:

var m sync.Map
m.Store("one", 1)

In short, the "assignment to entry in nil map" error is one of the common errors in the golang development process. We need to avoid this error by initializing the map and checking whether the map is empty. In addition, we can also use sync.Map to avoid this error.

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