正在尝试确定转换后的范围是否为空

试图构建代码，该代码采用向量，应用视图过滤器，然后进行转换，最后返回最后一个元素(如果存在(：

int foo()
{
std::vector<int> v = {0, 1, 5, 3, 8, 9};
auto r =
v
| view::filter([] (auto i) { return i % 2 == 0; })
| view::transform([] (auto i) { return i * 2; });
return r.empty() ? 0 : r.back();
}

编译会导致以下错误：

test.cpp: In function 'int foo()':
test.cpp:14:18: error: no matching function for call to 'ranges::v3::transform_view<ran
ges::v3::remove_if_view<ranges::v3::iterator_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >, __gnu_cxx::__normal_iterator<int*
, std::vector<int> > >, ranges::v3::logical_negate_<foo()::<lambda(auto:1)> > >, foo()::<lambda(auto:2)> >::empty()'
return r.empty() ? 0 : r.back();
^
In file included from range-v3/include/range/v3/view_facade.hpp:21:0,
from range-v3/include/range/v3/core.hpp:21,
from range-v3/include/range/v3/all.hpp:17,
from test.cpp:1:
range-v3/include/range/v3/view_interface.hpp:88:28: note: candidate: template<in
t _concept_requires_87, typename std::enable_if<((_concept_requires_87 == 43) || ((ranges::v3::cardinality)-1 >= 0)), int>::type <anonymous
> > constexpr bool ranges::v3::view_interface<Derived, <anonymous> >::empty() const [with int _concept_requires_87 = _concept_requires_87;
typename std::enable_if<((_concept_requires_87 == 43) || (Cardinality >= 0)), int>::type <anonymous> = <enumerator>; Derived = ranges::v3::
iter_transform_view<ranges::v3::remove_if_view<ranges::v3::iterator_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >, __gnu_cxx:
:__normal_iterator<int*, std::vector<int> > >, ranges::v3::logical_negate_<foo()::<lambda(auto:1)> > >, ranges::v3::indirected<foo()::<lamb
da(auto:2)> > >; ranges::v3::cardinality Cardinality = (ranges::v3::cardinality)-1]

因此，看起来transform_view缺少基数概念，而不管它是在变换的向量上操作。是否有一个运算符可以应用于允许此代码工作的范围？empty()需要基数似乎很奇怪，因为它只需要验证是否有任何元素，而不是提供确切的元素数量。