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flat_merge_godbolt.cpp
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flat_merge_godbolt.cpp
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#include <utility>
#include <functional>
#include <type_traits>
template<std::size_t... index, typename F>
auto applySequence(std::index_sequence<index...>, F&& f)
{
return f(std::integral_constant<std::size_t, index>{}...);
}
template<typename... Ts> struct TypeList {};
template<typename... Lhs, typename... Rhs>
auto operator+(TypeList<Lhs...>, TypeList<Rhs...>)
{
return TypeList<Lhs..., Rhs...>{};
}
template<typename T>
struct Tag { using type = T; };
template<typename... Lhs, typename Rhs>
auto operator+(TypeList<Lhs...>, Tag<Rhs>){ return TypeList<Lhs..., Rhs>{}; }
template<typename... Ts>
constexpr auto operator==(TypeList<Ts...>, TypeList<Ts...>){ return true; }
template<typename... Ts, typename... Other>
constexpr auto operator==(TypeList<Ts...>, TypeList<Other...>){ return false; }
template<int i>
using Int = std::integral_constant<int, i>;
template<typename F, typename G>
auto operator>>=(F f, G g) { return [f, g](auto arg){ return g(f(arg)); }; }
template<typename Int>
constexpr auto intLog2(Int x)
{
for(int i = 0;; x >>= 1, i++)
{
if(!x)
{
return i - 1;
}
}
}
template<std::size_t generation, std::size_t position>
struct split
{
template<typename... Ts>
constexpr auto operator()(TypeList<Ts...> tl) const
{
using Tup = std::tuple<Ts...>;
constexpr auto resultSize = 1 << (generation + 1);
return applySequence(
std::make_index_sequence<resultSize>{},
[](auto... i)
{
return TypeList<std::tuple_element_t<i + position * resultSize, Tup>...>{};
});
}
};
using Input = TypeList<bool, char, short, int>;
static_assert(std::is_same<decltype(split<0, 0>{}(Input{})), TypeList<bool, char> >::value, "");
static_assert(std::is_same<decltype(split<0, 1>{}(Input{})), TypeList<short, int> >::value, "");
using Input2 = TypeList<bool, char, short, int, long long, long long, long long, int>;
using Input3 = TypeList<long long, long long, long long, int>;
static_assert(std::is_same<decltype(split<1, 0>{}(Input2{})), Input>::value, "");
static_assert(std::is_same<decltype(split<1, 1>{}(Input2{})), Input3>::value, "");
template<std::size_t idx, typename T>
using Get = std::tuple_element_t<idx, T>;
template<std::size_t idx, typename Tuple, typename = void>
struct TupleIter: std::false_type {};
template<std::size_t idx, typename Tuple>
struct TupleIter<idx, Tuple, std::enable_if_t<(idx < std::tuple_size_v<Tuple>) > >:
std::true_type
{
using type = std::tuple_element_t<idx, Tuple>;
static constexpr auto advance(){ return TupleIter<idx + 1, Tuple>{}; }
static constexpr auto tag(){ return Tag<type>{}; }
};
template<typename L, typename R, typename Result>
struct Monad
{
L left;
R right;
Result result;
Monad(L l, R r, Result res): left(l), right(r), result(res){}
constexpr auto advanceLeft()
{
return ::Monad{left.advance(), right, result + left.tag()};
}
constexpr auto advanceRight()
{
return ::Monad{left, right.advance(), result + right.tag()};
}
};
template<typename Traits, typename Ts, typename Us>
struct Merge
{
template<std::size_t>
struct MergeImpl
{
template<typename State>
constexpr auto operator()(State s) const
{
if constexpr(s.left)
{
if constexpr(s.right)
{
if constexpr(Traits::compare(Traits::value(s.left.tag()), Traits::value(s.right.tag())))
{
return s.advanceLeft();
}
else
{
return s.advanceRight();
}
}
else
{
return s.advanceLeft();
}
}
else
{
return s.advanceRight();
}
}
};
constexpr auto operator()()
{
return applySequence(
std::make_index_sequence<std::tuple_size_v<Ts> + std::tuple_size_v<Us> >{},
[](auto... i)
{
return (MergeImpl<i>{} >>= ... >>= [](auto x){ return x; })(
Monad{TupleIter<0, Ts>{}, TupleIter<0, Us>{}, TypeList<>{}}).result;
});
}
};
template<typename Traits, typename... Ts, typename... Us>
constexpr auto merge(TypeList<Ts...>, TypeList<Us...>)
{
return Merge<Traits, std::tuple<Ts...>, std::tuple<Us...> >{}();
}
struct EfficientLayoutTraits
{
template<typename T>
static constexpr auto value(Tag<T>){ return sizeof(T); }
static constexpr std::less<> compare{};
};
static_assert(
std::is_same<
decltype(merge<EfficientLayoutTraits>(TypeList<>{}, TypeList<>{})),
TypeList<> >::value,
"");
static_assert(
std::is_same<
decltype(merge<EfficientLayoutTraits>(TypeList<>{}, TypeList<int>{})),
TypeList<int> >::value,
"");
static_assert(
std::is_same<
decltype(
merge<EfficientLayoutTraits>(TypeList<char>{}, TypeList<int>{})),
TypeList<char, int> >::value,
"");
static_assert(
std::is_same<
decltype(
merge<EfficientLayoutTraits>(
TypeList<bool, short, int>{},
TypeList<char, short, int>{})),
TypeList<char, bool, short, short, int, int> >::value,
"");
int main(){}