naive_put_in.ex

naive_put_in.ex

defmodule NaivePutIn do

  @doc """
  
  ### What problem does this solve?

  Sometimes I need a deeply nested map. Maps ALL THE WAY DOWN!
  If I can safely assume every step is a map, I should be able to do this:
  
  iex(0)> put_in(%{}, [:a, :b, :c], "V")

** (ArgumentError) could not put/update key :b on a nil value
    (elixir 1.10.4) lib/access.ex:365: Access.get_and_update/3
    (elixir 1.10.4) lib/map.ex:837: Map.get_and_update/3
    (elixir 1.10.4) lib/kernel.ex:2329: Kernel.put_in/3
    
  Behold! The solution:

  iex(1)> NaivePutIn.naive_put_in(%{}, [:a, :b, :c], "V")
  %{a: %{b: %{c: "V"}}}
  """

  def naive_put_in(m, path, v, acc \\ [])
  def naive_put_in(m, [], v, acc), do: put_in(m, acc, v)
  def naive_put_in(m,  [hd | tl], v,  acc) do
    curr_path = acc ++ [hd]
    m = case get_in(m, curr_path) do
      nil -> put_in(m, curr_path, %{})
      _ -> m
    end
    naive_put_in(m, tl, v, curr_path)
  end


end