Sprout/sprout/utility/value_holder.hpp

#ifndef SPROUT_UTILITY_VALUE_HOLDER_HPP
#define SPROUT_UTILITY_VALUE_HOLDER_HPP

#include <sprout/config.hpp>

namespace sprout {
	namespace detail {
		template<typename T>
		struct holder_helper {
		public:
			typedef T value_type;
			typedef T& reference;
			typedef T const& const_reference;
			typedef T const& mutable_or_const_reference;
			typedef T* pointer;
			typedef T const* const_pointer;
			typedef T const* mutable_or_const_pointer;
			typedef T const& param_type;
			typedef T holder_type;
		public:
			static SPROUT_CONSTEXPR holder_type const& hold(param_type p) {
				return p;
			}
			static SPROUT_CONSTEXPR reference ref(holder_type& r) {
				return r;
			}
			static SPROUT_CONSTEXPR const_reference ref(holder_type const& r) {
				return r;
			}
			static SPROUT_CONSTEXPR pointer ptr(holder_type& r) {
				return &r;
			}
			static SPROUT_CONSTEXPR const_pointer ptr(holder_type const& r) {
				return &r;
			}
		};
		template<typename T>
		struct holder_helper<T const> {
		public:
			typedef T value_type;
			typedef T const& reference;
			typedef T const& const_reference;
			typedef T const& mutable_or_const_reference;
			typedef T const* pointer;
			typedef T const* const_pointer;
			typedef T const* mutable_or_const_pointer;
			typedef T const& param_type;
			typedef T holder_type;
		public:
			static SPROUT_CONSTEXPR holder_type const& hold(param_type p) {
				return &p;
			}
			static SPROUT_CONSTEXPR reference ref(holder_type& r) {
				return *r;
			}
			static SPROUT_CONSTEXPR const_reference ref(holder_type const& r) {
				return *r;
			}
			static SPROUT_CONSTEXPR pointer ptr(holder_type& r) {
				return &r;
			}
			static SPROUT_CONSTEXPR const_pointer ptr(holder_type const& r) {
				return &r;
			}
		};
		template<typename T>
		struct holder_helper<T&> {
		public:
			typedef T value_type;
			typedef T& reference;
			typedef T const& const_reference;
			typedef T& mutable_or_const_reference;
			typedef T* pointer;
			typedef T const* const_pointer;
			typedef T* mutable_or_const_pointer;
			typedef T& param_type;
			typedef T* holder_type;
		public:
			static SPROUT_CONSTEXPR holder_type hold(param_type p) {
				return &p;
			}
			static SPROUT_CONSTEXPR reference ref(holder_type r) {
				return *r;
			}
			static SPROUT_CONSTEXPR pointer ptr(holder_type r) {
				return r;
			}
		};
		template<typename T>
		struct holder_helper<T const&> {
		public:
			typedef T value_type;
			typedef T const& reference;
			typedef T const& const_reference;
			typedef T const& mutable_or_const_reference;
			typedef T const* pointer;
			typedef T const* const_pointer;
			typedef T const* mutable_or_const_pointer;
			typedef T const& param_type;
			typedef T const* holder_type;
		public:
			static SPROUT_CONSTEXPR holder_type hold(param_type p) {
				return &p;
			}
			static SPROUT_CONSTEXPR reference ref(holder_type r) {
				return *r;
			}
			static SPROUT_CONSTEXPR pointer ptr(holder_type r) {
				return r;
			}
		};
	}	// namespace detail
	//
	// value_holder
	//
	template<typename T>
	class value_holder {
	public:
		typedef T type;
	private:
		typedef sprout::detail::holder_helper<type> helper_type;
		typedef typename helper_type::holder_type holder_type;
	public:
		typedef typename helper_type::value_type value_type;
		typedef typename helper_type::reference reference;
		typedef typename helper_type::const_reference const_reference;
		typedef typename helper_type::mutable_or_const_reference mutable_or_const_reference;
		typedef typename helper_type::pointer pointer;
		typedef typename helper_type::const_pointer const_pointer;
		typedef typename helper_type::mutable_or_const_pointer mutable_or_const_pointer;
		typedef typename helper_type::param_type param_type;
	private:
		holder_type holder_;
	public:
		value_holder() = default;
		explicit SPROUT_CONSTEXPR value_holder(param_type p)
			: holder_(helper_type::hold(p))
		{}
		operator reference() {
			return helper_type::ref(holder_);
		}
		SPROUT_CONSTEXPR operator const_reference() const {
			return helper_type::ref(holder_);
		}
		reference get() {
			return helper_type::ref(holder_);
		}
		SPROUT_CONSTEXPR mutable_or_const_reference get() const {
			return helper_type::ref(holder_);
		}
		pointer get_pointer() {
			return helper_type::ptr(holder_);
		}
		SPROUT_CONSTEXPR mutable_or_const_pointer get_pointer() const {
			return helper_type::ptr(holder_);
		}
	};
}	// namespace sprout

#endif // #ifndef SPROUT_UTILITY_VALUE_HOLDER_HPP