使用BOOST_PP_SEQ_FOREACH_R遞歸處理枚舉

Question

與我的問題相關的替代在switch語句中擴展模板的嘗試使Boost.Preprocessor在序列上進行嵌套插入。

#include <boost/preprocessor.hpp>
#include <iostream>

#define LASERTYPE_VALUES (EXCIMER)(GAS)(METALVAPOR)(SOLIDSTATE)(DYE)(SEMICONDUCTOR)(FREEELECTRON)(OTHER)

enum LaserType
{
  BOOST_PP_SEQ_ENUM(LASERTYPE_VALUES)
};

#define LT_NESTED(maR, maToplevelType, maNestedType)                    \
  std::cout << "Test nested: first=" << LaserType(maToplevelType) << " second=" << LaserType(maNestedType) << " \n";

#define LT_TOPLEVEL(maR, maUnused, maType)                              \
  std::cout << "Test toplevel: " << LaserType(maType) << " \n";         \
  BOOST_PP_SEQ_FOR_EACH_R(maR, LT_NESTED, maType, LASERTYPE_VALUES);

int main() {
  BOOST_PP_SEQ_FOR_EACH(LT_TOPLEVEL, %%, LASERTYPE_VALUES);
}

這導致此錯誤：

test-pp.cpp: In function ‘int main()’:
test-pp.cpp:15:32: error: ‘LT_NESTED’ was not declared in this scope
   BOOST_PP_SEQ_FOR_EACH_R(maR, LT_NESTED, maType, LASERTYPE_VALUES);
                                ^
/usr/include/boost/preprocessor/seq/for_each.hpp:49:57: note: in expansion of macro ‘LT_TOPLEVEL’
 # define BOOST_PP_SEQ_FOR_EACH_M_I(r, macro, data, seq) macro(r, data, BOOST_PP_SEQ_HEAD(seq))
                                                         ^
test-pp.cpp:4:39: error: ‘EXCIMER’ cannot be used as a function
 #define LASERTYPE_VALUES (EXCIMER)(GAS)(METALVAPOR)(SOLIDSTATE)(DYE)(SEMICONDUCTOR)(FREEELECTRON)(OTHER)
                                       ^
test-pp.cpp:15:51: note: in expansion of macro ‘LASERTYPE_VALUES’
   BOOST_PP_SEQ_FOR_EACH_R(maR, LT_NESTED, maType, LASERTYPE_VALUES);

重新排序宏沒有幫助。 這里有一些根本上的錯誤，這可能是微不足道的，但是我還沒有弄清楚如何做到這一點，也沒有看到任何不錯的例子。 如果有人有任何建議，我很想知道我在這里做錯了什么。

https://groups.google.com/forum/#!topic/boost-list/jhN4NE9VAtg表示我可能會遇到重入問題。 看起來我也許可以直接將BOOST_PP_FOR用於頂層宏。 如果有人舉個例子，那將非常有用。

Answer 1

我在https://groups.google.com/forum/#!topic/boost-devel-archive/Tbcs4nn4sPE中找到了一種解決方法，它提供了以下解決方案：

#include <boost/preprocessor.hpp>
#include <iostream>

#define LASERTYPE_VALUES (EXCIMER)(GAS)(METALVAPOR)(SOLIDSTATE)(DYE)(SEMICONDUCTOR)(FREEELECTRON)(OTHER)

enum LaserType
{
  BOOST_PP_SEQ_ENUM(LASERTYPE_VALUES)
};

#define PP_SEQ_FOR_EACH_R_ID() BOOST_PP_SEQ_FOR_EACH_R 
#define PP_DEFER(x) x BOOST_PP_EMPTY()

#define LT_NESTED(maR, maToplevelType, maNestedType)                    \
  std::cout << "Test nested: first=" << LaserType(maToplevelType) << " second=" << LaserType(maNestedType) << " \n";

#define LT_TOPLEVEL(maR, maUnused, maType)                              \
  std::cout << "Test toplevel: " << LaserType(maType) << " \n";         \
  PP_DEFER(PP_SEQ_FOR_EACH_R_ID)()(maR, LT_NESTED, maType, LASERTYPE_VALUES);

int main() {
  BOOST_PP_EXPAND(BOOST_PP_SEQ_FOR_EACH(LT_TOPLEVEL, %%, LASERTYPE_VALUES));
}

這有點深奧，但可以根據需要進行編譯和運行。