BLI_parameter_pack_utils.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once

 
#include <cstddef>
#include <tuple>
#include <type_traits>
 
namespace blender {

template<typename T, T Element> struct TypeForValue {
  static constexpr T value = Element;
};

template<typename T> struct TypeTag {
  using type = T;
};

template<typename T, T... Elements> struct ValueSequence {
  static constexpr size_t size() noexcept
  {
    return sizeof...(Elements);
  }

  template<size_t I> static constexpr T at_index()
  {
    static_assert(I < sizeof...(Elements));
    return std::tuple_element_t<I, std::tuple<TypeForValue<T, Elements>...>>::value;
  }

  template<T Element> static constexpr bool contains()
  {
    return ((Element == Elements) || ...);
  }
};

template<typename... T> struct TypeSequence {
  static constexpr size_t size() noexcept
  {
    return sizeof...(T);
  }

  template<size_t I> using at_index = std::tuple_element_t<I, std::tuple<T...>>;
};
 
namespace detail {
 
template<typename T, T Value, size_t... I>
inline ValueSequence<T, ((I == 0) ? Value : Value)...> make_value_sequence_impl(
    std::index_sequence<I...> /*indices*/)
{
  return {};
}
 
template<typename T, T Value1, T Value2, size_t... Value1Indices, size_t... I>
inline ValueSequence<T,
                     (ValueSequence<size_t, Value1Indices...>::template contains<I>() ? Value1 :
                                                                                        Value2)...>
make_two_value_sequence_impl(ValueSequence<size_t, Value1Indices...> /*value1_indices*/,
                             std::index_sequence<I...> /*indices*/)
{
  return {};
};
 
}  // namespace detail

template<typename T, T Value, size_t Size>
using make_value_sequence = decltype(detail::make_value_sequence_impl<T, Value>(
    std::make_index_sequence<Size>()));

template<typename T, T Value1, T Value2, size_t Size, size_t... Value1Indices>
using make_two_value_sequence = decltype(detail::make_two_value_sequence_impl<T, Value1, Value2>(
    ValueSequence<size_t, Value1Indices...>(), std::make_index_sequence<Size>()));
 
namespace parameter_pack_utils_static_tests {
enum class MyEnum { A, B };
static_assert(std::is_same_v<make_value_sequence<MyEnum, MyEnum::A, 3>,
                             ValueSequence<MyEnum, MyEnum::A, MyEnum::A, MyEnum::A>>);
static_assert(
    std::is_same_v<make_two_value_sequence<MyEnum, MyEnum::A, MyEnum::B, 5, 1, 2>,
                   ValueSequence<MyEnum, MyEnum::B, MyEnum::A, MyEnum::A, MyEnum::B, MyEnum::B>>);
}  // namespace parameter_pack_utils_static_tests
 
}  // namespace blender