c++ - 如何将 fusion 容器大小限制扩展到 50 以上？

Question

我想生成包含超过 50 个元素的 boost fusion 类型序列。 boost/fusion/container/vector/vector50.hpp的内容似乎暗示可以使用宏 BOOST_FUSION_DONT_USE_PREPROCESSED_FILES 以某种方式影响此限制。

我创建了以下简单程序，它将 int 推回到 boost::fusion::vector 类型指定的次数，然后将其转换为结果到 vector (触发错误)。

#include <boost/fusion/container.hpp>                                              
#include <boost/fusion/algorithm.hpp>                                              

#include <type_traits>                                                             

template <typename Sequence, int N>                                                
struct PushBack                                                                    
{                                                                                  
    using type = typename PushBack<typename boost::fusion::result_of::push_back<Sequence, int>::type, N-1>::type;
};                                                                                 

template <typename Sequence>                                                       
struct PushBack<Sequence, 0>                                                       
{                                                                                  
    using type = Sequence;                                                         
};                                                                                 

int main()                                                                         
{                                                                                  
    using NullVector = boost::fusion::vector<>;                                    
    using Sequence = boost::fusion::result_of::as_vector<typename PushBack<NullVector, 20>::type>::type; // this line triggers the error

    Sequence s;                                                                    
    return 0;                                                                      
}                          

当我使用 -D BOOST_FUSION_DONT_USE_PREPROCESSED_FILES -D FUSION_MAX_VECTOR_SIZE=100 运行它时，我收到大量错误，大致如下所示:

.../boost/fusion/container/generation/make_vector.hpp:105:25: error: ‘vector51’ does not name a type .../boost/fusion/container/generation/make_vector.hpp:105:25: error: ‘vector52’ does not name a type .../boost/fusion/container/generation/make_vector.hpp:105:25: error: ‘vector...’ does not name a type

显然我做的不对。如何将此限制扩展到 50 以上？我至少需要 150...

Answer 1

这是一个两步走的方法，首先定义:BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS在你的编译标志中，然后用 -DBOOST_MPL_LIMIT_VECTOR_SIZE=50 -DFUSION_MAX_VECTOR_SIZE=50 设置你需要的大小(最近的 10 个)

编辑:

你确实不走运，在标题中，即使你不使用预处理的标题，看起来它被这段代码限制为 50:

#if (FUSION_MAX_VECTOR_SIZE > 40)
#include <boost/fusion/container/vector/vector50.hpp>
#endif

然后做了真正愚蠢的事情:

#define BOOST_PP_FILENAME_1 <boost/fusion/container/vector/detail/vector_n.hpp>
#define BOOST_PP_ITERATION_LIMITS (41, 50)
#include BOOST_PP_ITERATE()

}}

嗯..我认为除了“修补”上面的代码之外没有别的办法..

EDIT2:好吧，如果有破解的意愿，显然有一种方法(无需修改 boost)，它确实带有一个巨大的免责声明 - 正确测试，编译，你可以访问超过 50 个元素，这就是我将提供的所有保修...

#include <iostream>

#define BOOST_MPL_LIMIT_VECTOR_SIZE 50
#define FUSION_MAX_VECTOR_SIZE 60

// This sets us up with mpl vector up to 50
#include <boost/mpl/vector.hpp>

// This adds the missing chunk - you should be able to expand this up to template depth
// This sets up the sequence of vectors (vector1 : T + vector0 etc.
#include <boost/fusion/sequence/intrinsic/begin.hpp>
namespace boost { namespace mpl {

#   define BOOST_PP_ITERATION_PARAMS_1 \
    (3,(51, 60, <boost/mpl/vector/aux_/numbered.hpp>))
#   include BOOST_PP_ITERATE()

}}
// This sets up the specializations
#define AUX778076_SEQUENCE_BASE_NAME vector
#   define AUX778076_SEQUENCE_LIMIT BOOST_MPL_LIMIT_VECTOR_SIZE
#   define AUX778076_SEQUENCE_CONVERT_CN_TO(z,n,TARGET) TARGET(BOOST_PP_CAT(C,n))
#   include <boost/mpl/aux_/sequence_wrapper.hpp>

// Include everuthing up to vector50
#define BOOST_FUSION_DONT_USE_PREPROCESSED_FILES
#include <boost/fusion/container/vector/vector50.hpp>

// Add the missing range
namespace boost
{
namespace fusion
{
struct vector_tag;
#define BOOST_PP_FILENAME_1 <boost/fusion/container/vector/detail/vector_n.hpp>
#define BOOST_PP_ITERATION_LIMITS (51, 60)
#include BOOST_PP_ITERATE()
}
}

// Declare the vector class using the FUSION_MAX_VECTOR_SIZE, as the types themselves have been declared above, all is
// good in the world of fusion
#include <boost/fusion/container/vector/vector.hpp>


// Test access
#include <boost/fusion/sequence/intrinsic/at_c.hpp>


int main()
{

  using Sequence = typename boost::fusion::vector<
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    int,
    double,
    std::string,
    std::string
 >;

 Sequence s;

 std::cout << boost::fusion::at_c<51>(s) << std::endl;

}

基本上，我上面所做的只是填充缺失的位(对于大于 50 的计数)，但根据需要实例化 mpl 和 fusion 的位。上面的操作顺序非常死板，如果有人可以进一步提炼它 - 请更新...

(注意:使用 gcc-4.8.2、boost-1.55、c++11 测试)