Reading the guides at this point http://elixir-lang.org/getting-started/keywords-and-maps.html#nested-data-structures We have an example that we can modify a specific data in a map using the put_in/2.

I’m curious how Elixir makes this work:

iex> users = [
  john: %{name: "John", age: 27, languages: ["Erlang", "Ruby", "Elixir"]},
  mary: %{name: "Mary", age: 29, languages: ["Elixir", "F#", "Clojure"]}
]
[john: %{age: 27, languages: ["Erlang", "Ruby", "Elixir"], name: "John"},
 mary: %{age: 29, languages: ["Elixir", "F#", "Clojure"], name: "Mary"}]

iex> users = put_in users[:john].age, 31
[john: %{age: 31, languages: ["Erlang", "Ruby", "Elixir"], name: "John"},
 mary: %{age: 29, languages: ["Elixir", "F#", "Clojure"], name: "Mary"}]

How Elixir returns the whole map? If we do not pass it to the function?

Thanks in advance.