如何同时定义多个模块？（宏尝试不起作用）

Question

我需要我的所有模型来实现特定的协议。我目前的尝试是MyApp.Convert定义了这个宏的模块：

defmodule ConvertMacro do
  @moduledoc """
  All model structs need to implement the convert interface and must be added
  here.
  """

  defmacro defimpl_convert_for(modules) do
    Enum.map(modules, fn module ->
      quote do
        defimpl Units.Convert, for: unquote(module) do
          require Units

          def to_standard_metric(struct) do
            Units.to_standard_metric_for_struct(unquote(module), struct)
          end

          def to_user_data(struct) do
            Units.to_user_data_for_struct(unquote(module), struct)
          end
        end
      end
    end)
  end
end

ConvertMacto.defimpl_convert_for([MyApp.User, MyApp.Block])

错误：

== Compilation error on file lib/protocols/units_convert.ex ==
** (UndefinedFunctionError) function ConvertMacro.defimpl_convert_for/1 is undefined or private. Did you mean one of:

      * defimpl_convert_for/1

    ConvertMacro.defimpl_convert_for([UdioDb.Block])
    (elixir) lib/kernel/parallel_compiler.ex:117: anonymous fn/4 in Kernel.ParallelCompiler.spawn_compilers/1

（错误信息其实有点多余）

有没有办法实现我想要做的事情，还是我只需要全部输入？

Answer 1

它实际上要简单得多，因为defimpl它本身就支持它：

defimpl FooProtocol, for: [Foo, Baz, Bar] do
  def protocol_function(x, y, z) do
    @for.some_function(x, y, z)
  end
end

该@for模块属性允许您访问该协议是为实现该模块。您可以在此处查看示例：https : //github.com/elixir-ecto/ecto/blob/master/lib/ecto/date_time.ex#L650-L662