Why Am I Getting a 'Runtime Error: Assignment to Entry in Nil Map' in Go?

Understanding "Runtime Error: Assignment to Entry in Nil Map"

When attempting to utilize Go's built-in map data structure, you may encounter the dreaded "runtime error: assignment to entry in nil map." This error stems from an attempt to assign a value to a non-existent key in a nil (or uninitialized) map.

In your specific case, you are trying to generate a YAML file from a map, where each key represents a "uid" and each value is a map containing information about an individual. However, your code encounters the runtime error.

Solution: Initializing the Inner Map

The issue arises because your inner map ("uid") is not initialized before you try to assign values to its keys (e.g., "kasi," "remya," and "nandan"). To resolve this, simply add the following line before the for loop:

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

This line initializes the inner map and associates it with the key "uid" in your outer map (m). Now, you can safely assign values to keys within the inner map:

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

Refined Code

Here is your code with the fix in place:

package main

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))
    m["uid"] = make(map[string]T)
    for _, name := range names {

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

    }
    fmt.Println(m)

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

    fmt.Println(string(y))
}

With this modification, you will no longer encounter the "runtime error: assignment to entry in nil map." Your code will successfully generate a YAML file with the desired structure.

The above is the detailed content of Why Am I Getting a 'Runtime Error: Assignment to Entry in Nil Map' in Go?. For more information, please follow other related articles on the PHP Chinese website!