带数组的BOOST_PP_REPEAT [英] BOOST_PP_REPEAT with array

问题描述

我有类似的结构：

struct E1
{
    typedef boost::tuple<  
     boost::optional< N::type_A >, // N - namespace
     boost::optional< N::type_B >,
     ...................
     boost::optional< N::type_X > //arbitrary number of, maximal is 7
     > data_type;


   // for access by name 
   boost::optional<N::type_A> const&  type_A() const { return boost::get<0>(data); }
   boost::optional<N::type_B> const&  type_B() const { return boost::get<1>(data); }
   .....................................
   boost::optional<N::type_X> const&  type_X() const { return boost::get<2>(data); }

   data_type data;
};

问：我如何使用BOOST预处理器创建此结构？对我来说只有type_A，type_B，...，type_X类型的名称。

Q: how I may create this structure using BOOST preprocessors? For me known only type_A, type_B, ..., type_X name of types.

它需要我，因为我必须创建很多这样的结构，只改变type_A ，type_B，... types。

It's need me, because I must create a lot of structures like that, only changing type_A, type_B, ... types.

在通常情况下，我可以使用boost预处理器数组或设置？

In common case, can I use boost preprocessor array or set?

推荐答案

您可以这样做：

#define TYPES (type_A)(type_B)(type_X)


#define GENERATE_TUPLE(maR, maNamespace, maIndex, maType) \
  BOOST_PP_COMMA_IF(maIndex) boost::optional<maNamespace :: maType>


#define GENERATE_GETTER(maR, maNamespace, maIndex, maType) \
  boost::optional<maNamespace :: maType> const& maType () const { return boost::get<maIndex>(data); }


struct E1
{
  typedef boost::tuple<
    BOOST_PP_SEQ_FOR_EACH_I(GENERATE_TUPLE, N, TYPES)
  > data_type;

  BOOST_PP_SEQ_FOR_EACH_I(GENERATE_GETTER, N, TYPES)

  data_type data;
};

N 参数对应于 maNamespace 参数。你当然可以以任何其他方式使用这个参数（它只是通过逐字传递），例如将 N 硬编码到宏中（并在参数中传递一个虚拟）编码，甚至其中的标识符 data 等。

The N argument corresponds to the maNamespace parameter. You can of course use this argument in any other way (it's just passed through verbatim), such as hardcoding N into the macros (and passing a dummy in the argument), or encoding even the identifier data in there, etc.

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