How Can I Safely Use Nested Maps in Go and Avoid Runtime Panics?

Nested Maps in Go: Common Pitfalls and Solutions

In Go, the zero value for maps is nil, meaning an uninitialized map. Storing values in a nil map results in a runtime panic. This can be seen in the following example:

func main() {
    var data = map[string]map[string]string{}
    data["a"]["w"] = "x"
    println(data)
}

This code will panic at runtime with the error "assignment to entry in nil map." To avoid this issue, explicitly initialize the map before assigning values to it, as shown below:

func main() {
    var data = map[string]map[string]string{}
    data["a"] = make(map[string]string)
    data["a"]["w"] = "x"
    println(data)
}

In this example, make(map[string]string) creates a new empty map of type map[string]string.

Another way to initialize nested maps is to use composite literals:

func main() {
    var data = map[string]map[string]string{
        "a": map[string]string{},
        "b": map[string]string{},
        "c": map[string]string{},
    }

    data["a"]["w"] = "x"
    println(data)
}

Both methods will correctly initialize the nested map and allow values to be stored without causing a runtime panic.

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