How to Resolve the Golang 'Runtime error: assignment to entry in nil map' Error?

Resolving "Runtime error: assignment to entry in nil map" with Golang Maps

When working with maps in Go, it's important to ensure that the maps are properly initialized before accessing or assigning values to them. The error message "runtime error: assignment to entry in nil map" indicates that you're attempting to modify a key-value pair in a map that hasn't been initialized.

Let's analyze the code snippet mentioned in the question:

import (
    "fmt"
    "gopkg.in/yaml.v2"
)

type T struct {
    cn     string
    street string
}

func main() {
    names := []string{"kasi", "remya", "nandan"}

    m := make(map[string]map[string]T, len(names))
    for _, name := range names {
        m["uid"][name] = T{cn: "Chaithra", street: "fkmp"}
    }
    fmt.Println(m)

    y, _ := yaml.Marshal(&m)

    fmt.Println(string(y))
}

The issue with the code lies in the following line:

m["uid"][name] = T{cn: "Chaithra", street: "fkmp"}

Here, you're attempting to access and modify the value at the specified keys "uid" and "name" in the map "m." However, you have not initialized the inner map for the key "uid." As a result, the map "m" has only one key, which is an empty map. When you try to access and modify the inner map at "m"uid"," the runtime encounters a nil pointer error because the key "uid" has not been initialized.

To resolve this issue, you need to initialize the inner map for the key "uid" before attempting to access and modify it. You can do this by adding the following line before the loop:

m["uid"] = make(map[string]T)

This line initializes an inner map for the key "uid" with no values, ensuring that you can access and modify it during the loop.

With this modification, your code will run successfully, generating the expected output. Remember, it's crucial to initialize maps before using them to avoid runtime errors.

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