我怎样才能同时为多个模块定义？ （宏尝试不工作）

Question

我需要我所有的模型来实现特定的协议。我现在的尝试是一个MyApp.Convert模块，这个宏定义：

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 

（错误消息实际上是有点多余）

有没有办法来实现我试图去做，还是我只需要输入一切呢？

Answer 1

它实际上是因为defimpl更简单的支持它本身：

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

的@for模块属性允许您访问该协议是为实现该模块。你可以在这里看到例子：https://github.com/elixir-ecto/ecto/blob/master/lib/ecto/date_time.ex#L650-L662