A map is Go’s dictionary-like collection for associating keys with values. Unlike slices and arrays, which serve as list-like collections, maps provide dictionary-style access. section 2.1.3
Maps can help represent valid options, but a slice is also suitable for listing values to validate. For JSON objects with unknown structure, use a map to access fields by key; known structures can instead be parsed into a struct. section 2.1.2 section 11.3
m := f.(map[string]interface{})
fmt.Println(m["firstName"])
After parsing arbitrary JSON into an interface, assert it as map[string]interface{} to retrieve a field such as firstName by key. section 11.3
