/usr/include/range/v3/utility/box.hpp is in librange-v3-dev 0.3.5-1.
This file is owned by root:root, with mode 0o644.
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// Range v3 library
//
// Copyright Eric Niebler 2013-present
// Copyright Casey Carter 2016
//
// 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_UTILITY_BOX_HPP
#define RANGES_V3_UTILITY_BOX_HPP
#include <utility>
#include <cstdlib>
#include <type_traits>
#include <meta/meta.hpp>
#include <range/v3/range_fwd.hpp>
#include <range/v3/utility/get.hpp>
#include <range/v3/utility/concepts.hpp>
namespace ranges
{
inline namespace v3
{
/// \addtogroup group-utility Utility
/// @{
///
template<typename T>
struct mutable_
{
mutable T value;
CONCEPT_REQUIRES(std::is_default_constructible<T>::value)
constexpr mutable_()
: value{}
{}
constexpr explicit mutable_(T const &t)
: value(t)
{}
constexpr explicit mutable_(T &&t)
: value(detail::move(t))
{}
mutable_ const &operator=(T const &t) const
{
value = t;
return *this;
}
mutable_ const &operator=(T &&t) const
{
value = detail::move(t);
return *this;
}
constexpr operator T &() const &
{
return value;
}
};
template<typename T, T v>
struct constant
{
constant() = default;
constexpr explicit constant(T const &)
{}
constant &operator=(T const &)
{
return *this;
}
constant const &operator=(T const &) const
{
return *this;
}
constexpr operator T() const
{
return v;
}
constexpr T exchange(T const &) const
{
return v;
}
};
static_assert(std::is_trivial<constant<int, 0>>::value, "Expected constant to be trivial");
/// \cond
namespace detail
{
// "box" has three different implementations that store a T differently:
enum class box_compress {
none, // Nothing special: get() returns a reference to a T member subobject
ebo, // Apply Empty Base Optimization: get() returns a reference to a T base subobject
coalesce // Coalesce all Ts into one T: get() returns a reference to a static T singleton
};
// Per N4582, lambda closures are *not*:
// - aggregates ([expr.prim.lambda]/4)
// - default constructible ([expr.prim.lambda]/p21)
// - copy assignable ([expr.prim.lambda]/p21)
template<typename Fn>
using could_be_lambda =
meta::bool_<
!std::is_default_constructible<Fn>::value &&
!std::is_copy_assignable<Fn>::value>;
template<typename>
constexpr box_compress box_compression_(...)
{
return box_compress::none;
}
template<typename T, typename = meta::if_<
meta::strict_and<std::is_empty<T>, meta::not_<detail::is_final<T>>
#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ == 6 && __GNUC_MINOR__ < 2
// GCC 6.0 & 6.1 find empty lambdas' implicit conversion to function pointer
// when doing overload resolution for function calls. That causes hard errors.
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71117
, meta::not_<could_be_lambda<T>>
#endif
>>>
constexpr box_compress box_compression_(long)
{
return box_compress::ebo;
}
#ifndef _MSC_VER
// MSVC pukes passing non-constant-expression objects to constexpr
// functions, so do not coalesce.
template<typename T, typename = meta::if_<
meta::strict_and<std::is_empty<T>, std::is_trivial<T>, std::is_default_constructible<T>>>>
constexpr box_compress box_compression_(int)
{
return box_compress::coalesce;
}
#endif
template<typename T>
constexpr box_compress box_compression()
{
return box_compression_<T>(0);
}
}
/// \endcond
template<typename Element, typename Tag = void, detail::box_compress = detail::box_compression<Element>()>
class box
{
Element value;
public:
CONCEPT_REQUIRES(std::is_default_constructible<Element>::value)
constexpr box()
noexcept(std::is_nothrow_default_constructible<Element>::value)
: value{}
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && std::is_convertible<E, Element>::value)>
constexpr box(E && e)
noexcept(std::is_nothrow_constructible<Element, E>::value)
: value(static_cast<E&&>(e))
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && !std::is_convertible<E, Element>::value)>
constexpr explicit box(E && e)
noexcept(std::is_nothrow_constructible<Element, E>::value)
: value(static_cast<E&&>(e))
{}
RANGES_CXX14_CONSTEXPR Element &get() & noexcept
{
return value;
}
constexpr Element const &get() const & noexcept
{
return value;
}
RANGES_CXX14_CONSTEXPR Element &&get() && noexcept
{
return detail::move(value);
}
};
template<typename Element, typename Tag>
class box<Element, Tag, detail::box_compress::ebo>
: Element
{
public:
CONCEPT_REQUIRES(std::is_default_constructible<Element>::value)
constexpr box()
noexcept(std::is_nothrow_default_constructible<Element>::value)
: Element{}
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && std::is_convertible<E, Element>::value)>
constexpr box(E && e)
noexcept(std::is_nothrow_constructible<Element, E>::value)
: Element(static_cast<E&&>(e))
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && !std::is_convertible<E, Element>::value)>
constexpr explicit box(E && e)
noexcept(std::is_nothrow_constructible<Element, E>::value)
: Element(static_cast<E&&>(e))
{}
RANGES_CXX14_CONSTEXPR Element &get() & noexcept
{
return *this;
}
constexpr Element const &get() const & noexcept
{
return *this;
}
RANGES_CXX14_CONSTEXPR Element &&get() && noexcept
{
return detail::move(*this);
}
};
template<typename Element, typename Tag>
class box<Element, Tag, detail::box_compress::coalesce>
{
static Element value;
public:
constexpr box() noexcept
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && std::is_convertible<E, Element>::value)>
constexpr box(E &&) noexcept
{}
template<typename E,
CONCEPT_REQUIRES_(std::is_constructible<Element, E>::value && !std::is_convertible<E, Element>::value)>
constexpr explicit box(E &&) noexcept
{}
RANGES_CXX14_CONSTEXPR Element &get() & noexcept
{
return value;
}
constexpr Element const &get() const & noexcept
{
return value;
}
RANGES_CXX14_CONSTEXPR Element &&get() && noexcept
{
return detail::move(value);
}
};
template<typename Element, typename Tag>
Element box<Element, Tag, detail::box_compress::coalesce>::value;
// Get by tag type
template<typename Tag, typename Element, detail::box_compress BC>
RANGES_CXX14_CONSTEXPR Element & get(box<Element, Tag, BC> & b) noexcept
{
return b.get();
}
template<typename Tag, typename Element, detail::box_compress BC>
constexpr Element const & get(box<Element, Tag, BC> const & b) noexcept
{
return b.get();
}
template<typename Tag, typename Element, detail::box_compress BC>
RANGES_CXX14_CONSTEXPR Element && get(box<Element, Tag, BC> && b) noexcept
{
return detail::move(b).get();
}
// Get by index
template<std::size_t I, typename Element, detail::box_compress BC>
RANGES_CXX14_CONSTEXPR Element & get(box<Element, meta::size_t<I>, BC> & b) noexcept
{
return b.get();
}
template<std::size_t I, typename Element, detail::box_compress BC>
constexpr Element const & get(box<Element, meta::size_t<I>, BC> const & b) noexcept
{
return b.get();
}
template<std::size_t I, typename Element, detail::box_compress BC>
RANGES_CXX14_CONSTEXPR Element && get(box<Element, meta::size_t<I>, BC> && b) noexcept
{
return detail::move(b).get();
}
/// @}
}
}
#endif
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