Why Does My Go Code Produce a 'assignment to entry in nil map' Error When Creating a YAML Map?

Addressing Runtime Error in Map Assignment

A developer encounters the runtime error "assignment to entry in nil map" while attempting to create a map and convert it to YAML. The code aims to generate a structure like this:

uid :
  kasi:
    cn: Chaithra
    street: fkmp
  nandan:
    cn: Chaithra
    street: fkmp
  remya:
    cn: Chaithra
    street: fkmp

The code in question is as follows:

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

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

    fmt.Println(string(y))
}

The error stems from the fact that the inner map, "uid", is not initialized before assigning values to its entries. To rectify this issue, the code can be modified as follows:

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) // Initialize the inner map here
    for _, name := range names {
        m["uid"][name] = T{cn: "Chaithra", street: "fkmp"}
    }
    fmt.Println(m)

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

    fmt.Println(string(y))
}

By initializing the inner map, we ensure that it exists and can be assigned values without raising the runtime error. This adjustment allows the code to generate the desired map structure and successfully convert it to YAML.

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