来自同一模块的Elixir结构默认值

Question

不知道如何创建一个结构，其默认值来自同一模块中的函数。下面是我的例子：

defmodule Poker.Deck do
  alias Poker.Deck.Card

  @values [:a, :"2", :"3", :"4", :"5", :"6", :"7", :"8", :"9", :"10", :j, :q, :k]
  @suits [:spades, :clubs, :diamonds, :hearts]

  def new do
   (for x <- @values, y <- @suits, do: %Card{value: x, suit: y})
   |> Enum.shuffle
  end

  # Putting this at the top or bottom still doesn't solve the problem...
  defstruct deck: __MODULE__.new, used: [], in_hand: []
end

编译时，它将返回以下内容：

== Compilation error on file lib/poker/deck.ex ==
** (UndefinedFunctionError) undefined function: Poker.Deck.new/0
    Poker.Deck.new()
    lib/poker/deck.ex:14: (module)
    (stdlib) erl_eval.erl:657: :erl_eval.do_apply/6
    (elixir) src/elixir.erl:163: :elixir.erl_eval/2
    (elixir) src/elixir.erl:156: :elixir.eval_forms/4

Answer 1

您可以利用defstruct只定义一个函数__struct__()的事实来实现这一点，该函数返回一个包含__struct__键的映射：

defmodule Poker.Deck do
  alias Poker.Deck.Card

  @values [:a, :"2", :"3", :"4", :"5", :"6", :"7", :"8", :"9", :"10", :j, :q, :k]
  @suits [:spades, :clubs, :diamonds, :hearts]

  def new do
   (for x <- @values, y <- @suits, do: %Card{value: x, suit: y})
   |> Enum.shuffle
  end

  def __struct__() do
    %{__struct__: __MODULE__, deck: __MODULE__.new(), used: [], in_hand: []}
  end
end

运行此命令将为每个新的%Poker.Deck{}实例提供一个全新的洗牌牌。