[英]Boost fusion sequence type and name identification for structs and class
我正在嘗試為我的一個項目使用boost fusion,我想知道如何獲取結構和類的類型名稱和變量名稱。
#include <typeinfo>
#include <string>
#include <iostream>
#include <boost/fusion/include/sequence.hpp>
#include <boost/fusion/include/algorithm.hpp>
#include <boost/fusion/include/vector.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/adapt_adt.hpp>
#include <boost/lexical_cast.hpp>
using namespace boost::fusion;
struct Foo
{
int integer_value;
bool boolean_value;
};
class Bar
{
int integer_value;
bool boolean_value;
public:
Bar(int i_val, bool b_val):integer_value(i_val),boolean_value(b_val) {}
int get_integer_value() const { return integer_value; }
void set_integer_value(int i_val) { integer_value = i_val; }
bool get_boolean_value() const { return boolean_value; }
void set_boolean_value(bool b_val) { boolean_value = b_val; }
};
BOOST_FUSION_ADAPT_STRUCT(
Foo,
(int, integer_value)
(bool, boolean_value)
)
BOOST_FUSION_ADAPT_ADT(
Bar,
(int, int, obj.get_integer_value() , obj.set_integer_value(val))
(bool, bool, obj.get_boolean_value(), obj.set_boolean_value(val))
)
struct DisplayMembers
{
template <typename T>
void operator()(T& t) const {
std::cout << typeid(t).name() << " : " << boost::lexical_cast<std::string>(t) << std::endl;
}
};
int main(int argc, char *argv[])
{
struct Foo f = { 33, false};
for_each(f, DisplayMembers());
Bar b(34,true);
for_each(b, DisplayMembers());
return 0;
}
在上面的例子中,結果是
int : 33
bool : 0
struct boost::fusion::extension::adt_attribute_proxy<class Bar,0,0> : 34
struct boost::fusion::extension::adt_attribute_proxy<class Bar,1,0> : 1
我希望結果為
int : integer_value : 33
bool : boolean_value : 0
int : integer_value : 34
bool : boolean_value : 1
有boost::fusion::extension::struct_member_name<S, N::value>
來訪問名稱。
這是我使用的通用融合對象訪問者:
namespace visitor {
template <typename Flavour, typename T> struct VisitorApplication;
namespace detail
{
template <typename V, typename Enable = void>
struct is_vector : boost::mpl::false_ { };
template <typename T>
struct is_vector<std::vector<T>, void> : boost::mpl::true_ { };
namespace iteration
{
// Iteration over a sequence
template <typename FusionVisitorConcept, typename S, typename N>
struct members_impl
{
// Type of the current member
typedef typename boost::fusion::result_of::value_at<S, N>::type current_t;
typedef typename boost::mpl::next<N>::type next_t;
typedef boost::fusion::extension::struct_member_name<S, N::value> name_t;
static inline void handle(FusionVisitorConcept& visitor, const S& s)
{
visitor.start_member(name_t::call());
VisitorApplication<FusionVisitorConcept, current_t>::handle(visitor, boost::fusion::at<N>(s));
visitor.finish_member(name_t::call());
members_impl<FusionVisitorConcept, S, next_t>::handle(visitor, s);
}
};
// End condition of sequence iteration
template <typename FusionVisitorConcept, typename S>
struct members_impl<FusionVisitorConcept, S, typename boost::fusion::result_of::size<S>::type>
{
static inline void handle(FusionVisitorConcept const&, const S&) { /*Nothing to do*/ }
};
// Iterate over struct/sequence. Base template
template <typename FusionVisitorConcept, typename S>
struct Struct : members_impl<FusionVisitorConcept, S, boost::mpl::int_<0>> {};
} // iteration
template <typename FusionVisitorConcept, typename T>
struct array_application
{
typedef array_application<FusionVisitorConcept, T> type;
typedef typename T::value_type value_type;
static inline void handle(FusionVisitorConcept& visitor, const T& t)
{
visitor.empty_array();
for (auto& el : t)
VisitorApplication<FusionVisitorConcept, value_type>::handle(visitor, el);
}
};
template <typename FusionVisitorConcept, typename T>
struct struct_application
{
typedef struct_application<FusionVisitorConcept, T> type;
static inline void handle(FusionVisitorConcept& visitor, const T& t)
{
visitor.empty_object();
iteration::Struct<FusionVisitorConcept, T>::handle(visitor, t);
}
};
template <typename FusionVisitorConcept, typename T, typename Enable = void>
struct value_application
{
typedef value_application<FusionVisitorConcept, T> type;
static inline void handle(FusionVisitorConcept& visitor, const T& t) {
visitor.value(t);
}
};
template <typename FusionVisitorConcept, typename T>
struct value_application<FusionVisitorConcept, boost::optional<T> >
{
typedef value_application<FusionVisitorConcept, boost::optional<T> > type;
static inline void handle(FusionVisitorConcept& visitor, const boost::optional<T>& t) {
if (t)
VisitorApplication<FusionVisitorConcept, T>::handle(visitor, *t);
else
; // perhaps some default action?
}
};
template <typename FusionVisitorConcept, typename T>
struct select_application
{
typedef
//typename boost::mpl::eval_if<boost::is_array<T>, boost::mpl::identity<array_application<FusionVisitorConcept, T>>,
typename boost::mpl::eval_if<detail::is_vector<T>, boost::mpl::identity<array_application <FusionVisitorConcept, T>>,
typename boost::mpl::eval_if<boost::fusion::traits::is_sequence<T>, boost::mpl::identity<struct_application<FusionVisitorConcept, T>>,
boost::mpl::identity<value_application<FusionVisitorConcept, T>>
> >::type type;
};
} // detail
template <typename FusionVisitorConcept, typename T>
struct VisitorApplication : public detail::select_application<FusionVisitorConcept, T>::type
{
};
}
template <typename FusionVisitorConcept, typename T>
void apply_fusion_visitor(FusionVisitorConcept& visitor, T const& o)
{
visitor::VisitorApplication<FusionVisitorConcept, T>::handle(visitor, o);
}
您可以通過提供訪問者來使用它,例如用於類似xml的輸出:
struct DisplayMemberVisitor {
typedef std::string result_type;
DisplayMemberVisitor() { ss << std::boolalpha; }
std::string complete() { return ss.str(); }
void start_member (const char* name) {
ss << "<" << name << ">";
}
void finish_member(const char* name) {
ss << "</" << name << ">";
}
template <typename T> void value(T const& value) {
ss << value;
}
void empty_object() { }
void empty_array() { }
private:
std::stringstream ss;
};
看看Live On Coliru它打印的地方(包括一些調試輸出):
<integer_value>33</integer_value><boolean_value>false</boolean_value><integer_value>34</integer_value><boolean_value>true</boolean_value>
請注意 ,ADT適配宏不包含名稱(因為沒有名稱)。 您可以很容易地創建一個宏FUSION_ADAPT_KEYD_ADT
,它也接受一個名稱並生成boost::fusion::extension::struct_member_name
的相關boost::fusion::extension::struct_member_name
。
這是一種簡單的方法,顯示了需要完成的少量工作。
#define MY_ADT_MEMBER_NAME(CLASSNAME, IDX, MEMBERNAME) \
namespace boost { namespace fusion { namespace extension { \
template <> struct struct_member_name<CLASSNAME, IDX> { typedef char const *type; static type call() { return #MEMBERNAME; } \
}; } } }
MY_ADT_MEMBER_NAME(Bar, 0, integer_value)
MY_ADT_MEMBER_NAME(Bar, 1, boolean_value)
這定義了一個宏來避免大部分重復。 如果你是一個BOOST_PP whizkid你可以以某種方式將它編織成一個adt_ex.hpp
標題,所以你可以說:
BOOST_FUSION_ADAPT_ADT(Bar, // NOTE THIS PSEUDO-CODE
(integer_value, int, int, obj.get_integer_value(), obj.set_integer_value(val))
(boolean_value, bool, bool, obj.get_boolean_value(), obj.set_boolean_value(val)))
現在這里是ADT改編的技巧Live On Coliru
¹萬一你感興趣的話,這是一個准備好的adt_ex樹的tarball(放入ads.hpp中): adt_ex.tgz作為起點。 它只是adt *但是宏和頭部保護重命名為adt_ex *
如果您使用的是C ++ 14,我會將答案簡化為更簡單的方法
#include <iostream>
#include <boost/fusion/include/algorithm.hpp>
#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/mpl/range_c.hpp>
struct MyStruct {
std::string foo;
double bar;
};
BOOST_FUSION_ADAPT_STRUCT(MyStruct,
foo,
bar)
namespace fuz = boost::fusion;
namespace mpl = boost::mpl;
int main(int argc, char* argv[]) {
MyStruct dummy{"yo",3.14};
fuz::for_each(mpl::range_c<
unsigned, 0, fuz::result_of::size<MyStruct>::value>(),
[&](auto index){
std::cout << "Name: "
<< fuz::extension::struct_member_name<MyStruct,index>::call()
<< " Value: "
<< fuz::at_c<index>(dummy) << std::endl;
});
}
輸出:
Name: foo Value: yo
Name: bar Value: 3.14
在coliru上看到它
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