/usr/include/range/v3/empty.hpp is in librange-v3-dev 0.3.5-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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// Range v3 library
//
// Copyright Eric Niebler 2014-present
//
// Use, modification and distribution is subject to the
// Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ericniebler/range-v3
//
#ifndef RANGES_V3_EMPTY_HPP
#define RANGES_V3_EMPTY_HPP
#include <range/v3/begin_end.hpp>
#include <range/v3/range_concepts.hpp>
#include <range/v3/size.hpp>
#include <range/v3/utility/static_const.hpp>
namespace ranges
{
inline namespace v3
{
/// \cond
namespace _empty_
{
struct fn
{
private:
// Prefer member if it is valid.
template<typename R>
static constexpr auto impl_(R &r, detail::priority_tag<2>)
RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
(
bool(r.empty())
)
// Fall back to size == 0.
template<typename R>
static constexpr auto impl_(R &r, detail::priority_tag<1>)
RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
(
ranges::size(r) == 0
)
// Fall further back to begin == end.
template<typename R,
CONCEPT_REQUIRES_(ForwardRange<R>())>
static constexpr bool impl_(R &r, detail::priority_tag<0>)
RANGES_AUTO_RETURN_NOEXCEPT
(
ranges::begin(r) == ranges::end(r)
)
public:
template<typename R>
constexpr auto operator()(R &&r) const
RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
(
fn::impl_(r, detail::priority_tag<2>{})
)
template<typename T, typename Fn = fn>
constexpr auto operator()(std::reference_wrapper<T> ref) const
RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
(
Fn()(ref.get())
)
template<typename T, typename Fn = fn>
constexpr auto operator()(ranges::reference_wrapper<T> ref) const
RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
(
Fn()(ref.get())
)
};
}
/// \endcond
/// \ingroup group-core
/// \return true if and only if range contains no elements.
RANGES_INLINE_VARIABLE(_empty_::fn, empty)
}
}
#endif
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