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#ifndef POLYMAKE_OPTIONAL_
#define POLYMAKE_OPTIONAL_
// Until we have migrated to C++17, we have to use std::experimental::optional.
// While GCC comes with a fully functional implementation,
// clang libc++ has a broken one in versions up to 6 and completely lacks it from version 7 upwards.
// Moreover, older clangs produce strange errors even in combination with libstdc++.
// For this configuration, we include a minimal implementation just covering our needs.
#if __cplusplus < 201703L
#if defined(__clang__) && (defined(_LIBCPP_STD_VER) || __clang_major__ < 4)
#include "polymake/internal/type_union.h"
namespace pm {
struct nullopt_t
{
enum class Construct { Token };
explicit constexpr nullopt_t(Construct) { }
};
constexpr nullopt_t nullopt { nullopt_t::Construct::Token };
template <typename T>
class optional
: private type_union<T> {
using base_t = type_union<T>;
public:
optional(nullopt_t) noexcept {}
explicit optional(const T& x)
: base_t(x) {}
explicit optional(T&& x)
: base_t(std::forward<T>(x)) {}
explicit operator bool() const noexcept
{
return this->valid();
}
const T& value() const&
{
if (const T* ptr = this->template as<T>())
return *ptr;
throw std::logic_error("bad optional access");
}
T& value() &
{
if (T* ptr = this->template as<T>())
return *ptr;
throw std::logic_error("bad optional access");
}
T&& value() &&
{
if (T* ptr = this->template as<T>())
return std::move(*ptr);
throw std::logic_error("bad optional access");
}
};
template <typename T>
optional<pure_type_t<T>> make_optional(T&& x)
{
return optional<pure_type_t<T>>{ std::forward<T>(x) };
}
}
namespace polymake {
using pm::optional;
using pm::nullopt;
using pm::make_optional;
}
#else // GCC or clang >= 4
# include <experimental/optional>
namespace polymake {
using std::experimental::optional;
using std::experimental::nullopt;
using std::experimental::make_optional;
}
namespace pm {
using std::experimental::optional;
using std::experimental::nullopt;
using std::experimental::make_optional;
}
#endif
#else
#include <optional>
namespace polymake {
using std::optional;
using std::nullopt;
using std::make_optional;
}
namespace pm {
using std::optional;
using std::nullopt;
using std::make_optional;
}
#endif
#endif // POLYMAKE_OPTIONAL_
// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
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