util/util.hpp

#pragma once

#include <stdint.h>

#include "../type/type.hpp"

namespace util {

template <typename T>
inline constexpr type::remove_reference_t<T> &&move(T &&t) noexcept
{
	return static_cast<type::remove_reference_t<T> &&>(t);
}

template <typename T>
inline constexpr T &&forward(type::remove_reference_t<T> &t) noexcept
{
	return static_cast<T &&>(t);
}

template <typename T>
inline constexpr T &&forward(type::remove_reference_t<T> &&t) noexcept
{
	static_assert(!type::is_lvalue_reference_v<T>, "Can not forward an rvalue as an lvalue.");
	return static_cast<T &&>(t);
}

template <typename T, T... Ints>
struct integer_sequence {
	using __type = integer_sequence;
	using value_type = T;

	static constexpr size_t size() noexcept
	{
		return sizeof...(Ints);
	}
};

template <size_t... Ints>
using index_sequence = integer_sequence<size_t, Ints...>;

namespace detail {

template <typename T, typename Seq1, typename Seq2>
struct concat;

template <typename T, T... Ints1, T... Ints2>
struct concat<T, integer_sequence<T, Ints1...>, integer_sequence<T, Ints2...>>
    : integer_sequence<T, Ints1..., (sizeof...(Ints1) + Ints2)...> {
};

// uint64_t because this must be able to hold all possible sizes and cannot be T, because then the specialization for 0
// and 1 are not possible
template <typename T, uint64_t N>
struct gen_integer_sequence : detail::concat<T, typename gen_integer_sequence<T, N / 2>::__type,
                                             typename gen_integer_sequence<T, N - N / 2>::__type> {
};

template <typename T>
struct gen_integer_sequence<T, 0> : integer_sequence<T> {
};

template <typename T>
struct gen_integer_sequence<T, 1> : integer_sequence<T, 0> {
};

} // namespace detail

template <typename T, T N>
struct make_integer_sequence : detail::gen_integer_sequence<T, N> {
	static_assert(N >= 0, "Integer sequence cannot be negative");
};

template <size_t N>
using make_index_sequence = make_integer_sequence<size_t, N>;

template <typename... T>
using index_sequence_for = make_index_sequence<sizeof...(T)>;

// Not part of <utility>, but very useful

namespace detail {

template <typename T, T Offset, T... Ints>
inline constexpr integer_sequence<T, (Offset + Ints)...> add_offset(integer_sequence<T, Ints...>)
{
	return {};
}

} // namespace detail

template <typename T, T Offset, T N>
inline constexpr auto make_offset_integer_sequence()
{
	return detail::add_offset<T, Offset>(make_integer_sequence<T, N>{});
}

template <size_t Offset, size_t N>
inline constexpr auto make_offset_index_sequence()
{
	return make_offset_integer_sequence<size_t, Offset, N>();
}

} // namespace util