我可以访问GCC 10并使用-std=c++20进行编译，并且需要generatecache1,concat等视图，这些视图直到可能的c++ 23才被指定。
我在下面写了一个简单的程序，使用range-v3输出'1 2 2 3 3 3'。我尝试混合range-v3视图和rangesinclude的视图，但没有成功。"范围"库似乎期望视图从view_interface继承，所以我创建了一个wrap_view_t来帮助解决这个问题(未显示)。要查看工作范围v3代码，请注释以下行:
//#define MIX_RANGES_WITH_RANGE_V3
代码:
#include <iostream>
#define MIX_RANGES_WITH_RANGE_V3
#ifdef MIX_RANGES_WITH_RANGE_V3
#include <ranges>
namespace test { using namespace std::ranges; }
#else
#include <range/v3/view/all.hpp>
#include <range/v3/view/interface.hpp>
#include <range/v3/view/join.hpp>
#include <range/v3/view/take_while.hpp>
#include <range/v3/view/transform.hpp>
namespace test { using namespace ranges; }
#endif
#include <range/v3/view/generate.hpp>
#include <range/v3/view/cache1.hpp>
auto my_view()
{
auto gen{ ranges::views::generate( [ n = 0 ]() mutable
{
return std::vector< int >( ++n, n );
} )
| ranges::views::cache1
};
return std::move( gen )
| test::views::take_while( []( auto const & value ) { return value.size() < 4; } )
| test::views::transform( []( auto const & value )
{ return test::views::all( value ); } );
}
int main()
{
for( auto const value : my_view() | test::views::join )
{
std::cout <<value <<" ";
}
std::cout <<std::endl;
return 0;
}
和编译错误
test_rng/test_rng_simpler.C: In function ‘auto my_view()’:
test_rng/test_rng_simpler.C:28:3: error: no match for ‘operator|’ (operand types are ‘std::remove_reference<ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >&>::type’ {aka ‘ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >’} and ‘std::ranges::views::__adaptor::_RangeAdaptorClosure<std::ranges::views::__adaptor::_RangeAdaptor<_Callable>::operator()<{my_view()::<lambda(const auto:16&)>}>::<lambda(_Range&&)> >’)
27 | return std::move( gen )
| ~~~~~~~~~~~~~~~~
| |
| std::remove_reference<ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >&>::type {aka ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >}
28 | | test::views::take_while( []( auto const & value ) { return value.size() < 4; } )
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
| std::ranges::views::__adaptor::_RangeAdaptorClosure<std::ranges::views::__adaptor::_RangeAdaptor<_Callable>::operator()<{my_view()::<lambda(const auto:16&)>}>::<lambda(_Range&&)> >
In file included from test_rng/test_rng_simpler.C:6:
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:1180:4: note: candidate: ‘template<class _Tp> constexpr auto std::ranges::views::__adaptor::operator|(const std::ranges::views::__adaptor::_RangeAdaptorClosure<_Callable>&, const std::ranges::views::__adaptor::_RangeAdaptorClosure<std::ranges::views::__adaptor::_RangeAdaptor<_Callable>::operator()<{my_view()::<lambda(const auto:16&)>}>::<lambda(_Range&&)> >&)’
1180 | operator|(const _RangeAdaptorClosure<_Tp>& __x,
| ^~~~~~~~
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:1180:4: note: template argument deduction/substitution failed:
test_rng/test_rng_simpler.C:28:84: note: ‘std::remove_reference<ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >&>::type’ {aka ‘ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >’} is not derived from ‘const std::ranges::views::__adaptor::_RangeAdaptorClosure<_Callable>’
28 | | test::views::take_while( []( auto const & value ) { return value.size() < 4; } )
| ^
In file included from test_rng/test_rng_simpler.C:6:
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:1175:4: note: candidate: ‘constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, const std::ranges::views::__adaptor::_RangeAdaptorClosure<_Callable>&) [with _Range = ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >; _Callable = std::ranges::views::__adaptor::_RangeAdaptor<_Callable>::operator()<{my_view()::<lambda(const auto:16&)>}>::<lambda(_Range&&)>]’
1175 | operator|(_Range&& __r, const _RangeAdaptorClosure& __o)
| ^~~~~~~~
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:1175:4: note: constraints not satisfied
test_rng/test_rng_simpler.C: In instantiation of ‘constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, const std::ranges::views::__adaptor::_RangeAdaptorClosure<_Callable>&) [with _Range = ranges::cache1_view<ranges::generate_view<my_view()::<lambda()> > >; _Callable = std::ranges::views::__adaptor::_RangeAdaptor<_Callable>::operator()<{my_view()::<lambda(const auto:16&)>}>::<lambda(_Range&&)>]’:
test_rng/test_rng_simpler.C:28:84: required from here
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:78:13: required for the satisfaction of ‘viewable_range<_Range>’ [with _Range = ranges::cache1_view<ranges::generate_view<my_view::._anon_131> >]
/opt/rh/devtoolset-10/root/usr/include/c++/10/ranges:79:31: note: no operand of the disjunction is satisfied
79 | && (borrowed_range<_Tp> || view<remove_cvref_t<_Tp>>);
| ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
也许我应该坚持'范围v3'，直到我需要的所有视图都可以在'范围'包括?
由于range-v3中的适配器不继承ranges::view_interface，这使得它们在标准中不是view。为了避免悬空的危险，标准禁止将没有对borrowed_range或view(在您的示例中为gen)建模的range传递到管道中。
您需要做的是使用一个临时变量来接受generate，使其成为左值range，这样就可以满足borrowed_range，并且可以使用标准的管道操作:
#include <iostream>
#include <ranges>
#include <range/v3/view/generate.hpp>
#include <range/v3/view/cache1.hpp>
int main() {
auto gen = ranges::views::generate([n = 0]() mutable {
return std::vector<int>(++n, n);
}) | ranges::views::cache1;
for (auto const value : gen
| std::views::take_while([](auto const& value) { return value.size() < 4; })
| std::views::transform([](auto const& value) { return std::views::all(value); })
| std::views::join) {
std::cout <<value <<" ";
}
}
演示。