gistfile1.ex

defmodule Instrument do
  @zero :decimal_conv.number("0")
  @struct symbol: nil, name: "", value: @zero
  defstruct @struct
  @keys Enum.sort(@struct |> Map.keys |> List.delete(:__struct__))
  for k <- @keys do
    def __atomize__({unquote(Atom.to_string(k)), v}, acc) do
      Dict.put(acc, unquote(k), v)
    end
    def __atomize__({unquote(k), v}, acc) do
      Dict.put(acc, unquote(k), v)
    end
  end
  def __atomize__(_, acc), do: acc

  def new(kv) do
    kv = Enum.reduce(kv, %{}, &__atomize__/2)
    kv = Dict.update(kv, :value, @zero,
      fn(v) -> :decimal_conv.number(v) end)
    struct(__MODULE__, kv)
  end

  def value(record, amount) do
    %{record | value: :decimal_conv.number(amount)}
  end

  def struct?(%{__struct__: struct} = map, struct) do
    map = Map.delete(map, :__struct__) # To prevent protocol dispatch
    atomized_map = Enum.reduce(map, %{}, &__atomize__/2)
    Enum.sort(Map.keys(atomized_map)) == @keys
  end
  def struct?(_, _), do: false
  def struct?(map), do: is_struct(map, __MODULE__)
end