Elixir - Sample of struct + API

user.ex

defmodule User do
  defstruct name: nil, gender: nil, roles: [:normal]

  defmodule NameError do
    defexception message: "Name is too short"
  end

  def add_name(%User{} = user, name) when is_binary(name) do
    try do
      validate!(name: name)
      %{user | name: name}
    catch
      kind, %User.NameError{message: message} ->
        {kind, message}
    end
  end

  def validate!(name: name) do
    unless String.length(name) > 1, do: raise NameError
  end
end