132 lines
3.7 KiB
C++
132 lines
3.7 KiB
C++
/* SPDX-FileCopyrightText: 2023 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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#pragma once
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/** \file
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* \ingroup bli
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*
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* C++ has a feature called "parameter packs" which allow building variadic templates.
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* This file has some utilities to work with such parameter packs.
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*/
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#include <tuple>
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#include <type_traits>
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#include "BLI_utildefines.h"
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namespace blender {
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/**
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* A type that encodes a specific value.
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*/
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template<typename T, T Element> struct TypeForValue {
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static constexpr T value = Element;
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};
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/**
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* A struct that allows passing in a type as a function parameter.
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*/
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template<typename T> struct TypeTag {
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using type = T;
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};
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/**
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* A type that encodes a list of values of the same type.
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* This is similar to #std::integer_sequence, but a bit more general. It's main purpose it to also
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* support enums instead of just ints.
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*/
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template<typename T, T... Elements> struct ValueSequence {
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/**
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* Get the number of elements in the sequence.
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*/
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static constexpr size_t size() noexcept
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{
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return sizeof...(Elements);
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}
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/**
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* Get the element at a specific index.
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*/
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template<size_t I> static constexpr T at_index()
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{
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static_assert(I < sizeof...(Elements));
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return std::tuple_element_t<I, std::tuple<TypeForValue<T, Elements>...>>::value;
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}
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/**
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* Return true if the element is in the sequence.
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*/
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template<T Element> static constexpr bool contains()
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{
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return ((Element == Elements) || ...);
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}
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};
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/**
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* A type that encodes a list of types.
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* #std::tuple can also encode a list of types, but has a much more complex implementation.
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*/
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template<typename... T> struct TypeSequence {
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/**
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* Get the number of types in the sequence.
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*/
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static constexpr size_t size() noexcept
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{
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return sizeof...(T);
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}
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/**
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* Get the type at a specific index.
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*/
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template<size_t I> using at_index = std::tuple_element_t<I, std::tuple<T...>>;
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};
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namespace detail {
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template<typename T, T Value, size_t... I>
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inline ValueSequence<T, ((I == 0) ? Value : Value)...> make_value_sequence_impl(
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std::index_sequence<I...> /*indices*/)
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{
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return {};
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}
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template<typename T, T Value1, T Value2, size_t... Value1Indices, size_t... I>
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inline ValueSequence<T,
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(ValueSequence<size_t, Value1Indices...>::template contains<I>() ? Value1 :
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Value2)...>
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make_two_value_sequence_impl(ValueSequence<size_t, Value1Indices...> /*value1_indices*/,
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std::index_sequence<I...> /*indices*/)
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{
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return {};
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};
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} // namespace detail
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/**
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* Utility to create a #ValueSequence that has the same value at every index.
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*/
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template<typename T, T Value, size_t Size>
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using make_value_sequence = decltype(detail::make_value_sequence_impl<T, Value>(
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std::make_index_sequence<Size>()));
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/**
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* Utility to create a #ValueSequence that contains two different values. The indices of where the
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* first value should be used are passed in.
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*/
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template<typename T, T Value1, T Value2, size_t Size, size_t... Value1Indices>
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using make_two_value_sequence = decltype(detail::make_two_value_sequence_impl<T, Value1, Value2>(
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ValueSequence<size_t, Value1Indices...>(), std::make_index_sequence<Size>()));
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namespace parameter_pack_utils_static_tests {
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enum class MyEnum { A, B };
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static_assert(std::is_same_v<make_value_sequence<MyEnum, MyEnum::A, 3>,
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ValueSequence<MyEnum, MyEnum::A, MyEnum::A, MyEnum::A>>);
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static_assert(
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std::is_same_v<make_two_value_sequence<MyEnum, MyEnum::A, MyEnum::B, 5, 1, 2>,
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ValueSequence<MyEnum, MyEnum::B, MyEnum::A, MyEnum::A, MyEnum::B, MyEnum::B>>);
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} // namespace parameter_pack_utils_static_tests
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} // namespace blender
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