boost.tuple与C ++ 0x variadic模板兼容吗?
-
01-10-2019 - |
题
我正在玩Variadic模板(GCC 4.5),并遇到了这个问题:
template <typename... Args>
boost::tuple<Args...>
my_make_tuple(Args... args)
{
return boost::tuple<Args...>(args...);
}
int main (void)
{
boost::tuple<int, char> t = my_make_tuple(8, 'c');
}
GCC错误消息:
sorry, unimplemented: cannot expand 'Arg ...' into a fixed-length argument list
In function 'int my_make_tuple(Arg ...)'
如果我更换每一次 boost::tuple
经过 std::tuple
, ,它可以很好地编译。
Boost Tuple实施中是否有问题?还是这是GCC错误?
我必须暂时坚持boost.tuple。你知道有能力吗?
谢谢。
解决方案
似乎不喜欢扩展 Args...
到 T1, T2, T3, ..., T9
作为Boost。
作为解决方法,使用不需要这种扩展的结构:
#include <boost/tuple/tuple.hpp>
template <typename... Args>
auto my_make_tuple(Args... args) -> decltype(boost::make_tuple(args...))
{
return {args...};
}
int main (void)
{
boost::tuple<int, char> t = my_make_tuple(8, 'c');
}
另一个选择可能是手动进行扩展,看到 boost::tuple
最多支持10个参数。
#include <boost/tuple/tuple.hpp>
template <unsigned, class, class...> struct nth_argument;
template <unsigned N, class Default, class T, class... Args>
struct nth_argument<N, Default, T, Args...>
{
typedef typename nth_argument<N - 1, Default, Args...>::type type;
};
template <class Default, class T, class... Args>
struct nth_argument<0, Default, T, Args...>
{
typedef T type;
};
template <unsigned N, class Default>
struct nth_argument<N, Default>
{
typedef Default type;
};
template <typename ...Args>
struct tuple_from_var_template
{
typedef boost::tuple<
typename nth_argument<0, boost::tuples::null_type, Args...>::type,
typename nth_argument<1, boost::tuples::null_type, Args...>::type,
typename nth_argument<2, boost::tuples::null_type, Args...>::type,
typename nth_argument<3, boost::tuples::null_type, Args...>::type,
typename nth_argument<4, boost::tuples::null_type, Args...>::type,
typename nth_argument<5, boost::tuples::null_type, Args...>::type,
typename nth_argument<6, boost::tuples::null_type, Args...>::type,
typename nth_argument<7, boost::tuples::null_type, Args...>::type,
typename nth_argument<8, boost::tuples::null_type, Args...>::type,
typename nth_argument<9, boost::tuples::null_type, Args...>::type
> type;
};
template <typename... Args>
typename tuple_from_var_template<Args...>::type my_make_tuple(Args... args)
{
return typename tuple_from_var_template<Args...>::type(args...);
}
int main (void)
{
boost::tuple<int, char> t = my_make_tuple(8, 'c');
}
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