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/* SPDX-License-Identifier: GPL-2.0-or-later */
#pragma once
/** \file
* \ingroup bli
*
* C++ has a feature called "parameter packs" which allow building variadic templates.
* This file has some utilities to work with such parameter packs.
*/
#include <tuple>
#include <type_traits>
#include "BLI_utildefines.h"
namespace blender {
/**
* A type that encodes a specific value.
*/
template<typename T, T Element> struct TypeForValue {
static constexpr T value = Element;
};
/**
* A type that encodes a list of values of the same type.
* This is similar to #std::integer_sequence, but a bit more general. It's main purpose it to also
* support enums instead of just ints.
*/
template<typename T, T... Elements> struct ValueSequence {
/**
* Get the number of elements in the sequence.
*/
static constexpr size_t size() noexcept
{
return sizeof...(Elements);
}
/**
* Get the element at a specific index.
*/
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;
}
/**
* Return true if the element is in the sequence.
*/
template<T Element> static constexpr bool contains()
{
return ((Element == Elements) || ...);
}
};
/**
* A type that encodes a list of types.
* #std::tuple can also encode a list of types, but has a much more complex implementation.
*/
template<typename... T> struct TypeSequence {
/**
* Get the number of types in the sequence.
*/
static constexpr size_t size() noexcept
{
return sizeof...(T);
}
/**
* Get the type at a specific index.
*/
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
/**
* Utility to create a #ValueSequence that has the same value at every index.
*/
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>()));
/**
* Utility to create a #ValueSequence that contains two different values. The indices of where the
* first value should be used are passed in.
*/
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
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