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Diffstat (limited to 'source/blender/blenlib/BLI_any.hh')
| -rw-r--r-- | source/blender/blenlib/BLI_any.hh | 319 |
1 files changed, 319 insertions, 0 deletions
diff --git a/source/blender/blenlib/BLI_any.hh b/source/blender/blenlib/BLI_any.hh new file mode 100644 index 00000000000..0fc5de5540f --- /dev/null +++ b/source/blender/blenlib/BLI_any.hh @@ -0,0 +1,319 @@ +/* + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software Foundation, + * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + */ + +#pragma once + +/** \file + * \ingroup bli + * + * A #blender::Any is a type-safe container for single values of any copy constructible type. + * It is similar to #std::any but provides the following two additional features: + * - Adjustable inline buffer capacity and alignment. #std::any has a small inline buffer in most + * implementations as well, but its size is not guaranteed. + * - Can store additional user-defined type information without increasing the stack size of #Any. + */ + +#include <algorithm> +#include <utility> + +#include "BLI_memory_utils.hh" + +namespace blender { + +namespace detail { + +/** + * Contains function pointers that manage the memory in an #Any. + * Additional type specific #ExtraInfo can be embedded here as well. + */ +template<typename ExtraInfo> struct AnyTypeInfo { + void (*copy_construct)(void *dst, const void *src); + void (*move_construct)(void *dst, void *src); + void (*destruct)(void *src); + const void *(*get)(const void *src); + ExtraInfo extra_info; + + /** + * Used when #T is stored directly in the inline buffer of the #Any. + */ + template<typename T> static const AnyTypeInfo &get_for_inline() + { + static AnyTypeInfo funcs = {[](void *dst, const void *src) { new (dst) T(*(const T *)src); }, + [](void *dst, void *src) { new (dst) T(std::move(*(T *)src)); }, + [](void *src) { ((T *)src)->~T(); }, + [](const void *src) { return src; }, + ExtraInfo::template get<T>()}; + return funcs; + } + + /** + * Used when #T can't be stored directly in the inline buffer and is stored in a #std::unique_ptr + * instead. In this scenario, the #std::unique_ptr is stored in the inline buffer. + */ + template<typename T> static const AnyTypeInfo &get_for_unique_ptr() + { + using Ptr = std::unique_ptr<T>; + static AnyTypeInfo funcs = { + [](void *dst, const void *src) { new (dst) Ptr(new T(**(const Ptr *)src)); }, + [](void *dst, void *src) { new (dst) Ptr(new T(std::move(**(Ptr *)src))); }, + [](void *src) { ((Ptr *)src)->~Ptr(); }, + [](const void *src) -> const void * { return &**(const Ptr *)src; }, + ExtraInfo::template get<T>()}; + return funcs; + } + + /** + * Used when the #Any does not contain any type currently. + */ + static const AnyTypeInfo &get_for_empty() + { + static AnyTypeInfo funcs = {[](void *UNUSED(dst), const void *UNUSED(src)) {}, + [](void *UNUSED(dst), void *UNUSED(src)) {}, + [](void *UNUSED(src)) {}, + [](const void *UNUSED(src)) -> const void * { return nullptr; }, + ExtraInfo{}}; + return funcs; + } +}; + +/** + * Dummy extra info that is used when no additional type information should be stored in the #Any. + */ +struct NoExtraInfo { + template<typename T> static NoExtraInfo get() + { + return {}; + } +}; + +} // namespace detail + +template< + /** + * Either void or a struct that contains data members for additional type information. + * The struct has to have a static `ExtraInfo get<T>()` method that initializes the struct + * based on a type. + */ + typename ExtraInfo = void, + /** + * Size of the inline buffer. This allows types that are small enough to be stored directly + * inside the #Any without an additional allocation. + */ + size_t InlineBufferCapacity = 8, + /** + * Required minimum alignment of the inline buffer. If this is smaller than the alignment + * requirement of a used type, a separate allocation is necessary. + */ + size_t Alignment = 8> +class Any { + private: + /* Makes it possible to use void in the template parameters. */ + using RealExtraInfo = + std::conditional_t<std::is_void_v<ExtraInfo>, detail::NoExtraInfo, ExtraInfo>; + using Info = detail::AnyTypeInfo<RealExtraInfo>; + + /** + * Inline buffer that either contains nothing, the stored value directly, or a #std::unique_ptr + * to the value. + */ + AlignedBuffer<std::max(InlineBufferCapacity, sizeof(std::unique_ptr<int>)), Alignment> buffer_{}; + + /** + * Information about the type that is currently stored. + */ + const Info *info_ = &Info::get_for_empty(); + + public: + /** Only copy constructible types can be stored in #Any. */ + template<typename T> static constexpr inline bool is_allowed_v = std::is_copy_constructible_v<T>; + + /** + * Checks if the type will be stored in the inline buffer or if it requires a separate + * allocation. + */ + template<typename T> + static constexpr inline bool is_inline_v = std::is_nothrow_move_constructible_v<T> && + sizeof(T) <= InlineBufferCapacity && + alignof(T) <= Alignment; + + /** + * Checks if #T is the same type as this #Any, because in this case the behavior of e.g. the + * assignment operator is different. + */ + template<typename T> + static constexpr inline bool is_same_any_v = std::is_same_v<std::decay_t<T>, Any>; + + private: + template<typename T> const Info &get_info() const + { + using DecayT = std::decay_t<T>; + static_assert(is_allowed_v<DecayT>); + if constexpr (is_inline_v<DecayT>) { + return Info::template get_for_inline<DecayT>(); + } + else { + return Info::template get_for_unique_ptr<DecayT>(); + } + } + + public: + Any() = default; + + Any(const Any &other) : info_(other.info_) + { + info_->copy_construct(&buffer_, &other.buffer_); + } + + /** + * \note The #other #Any will not be empty afterwards if it was not before. Just its value is in + * a moved-from state. + */ + Any(Any &&other) noexcept : info_(other.info_) + { + info_->move_construct(&buffer_, &other.buffer_); + } + + /** + * Constructs a new #Any that contains the given type #T from #args. The #std::in_place_type_t is + * used to disambiguate this and the copy/move constructors. + */ + template<typename T, typename... Args> explicit Any(std::in_place_type_t<T>, Args &&...args) + { + using DecayT = std::decay_t<T>; + static_assert(is_allowed_v<DecayT>); + info_ = &this->template get_info<DecayT>(); + if constexpr (is_inline_v<DecayT>) { + /* Construct the value directly in the inline buffer. */ + new (&buffer_) DecayT(std::forward<Args>(args)...); + } + else { + /* Construct the value in a new allocation and store a #std::unique_ptr to it in the inline + * buffer. */ + new (&buffer_) std::unique_ptr<DecayT>(new DecayT(std::forward<Args>(args)...)); + } + } + + /** + * Constructs a new #Any that contains the given value. + */ + template<typename T, typename X = std::enable_if_t<!is_same_any_v<T>, void>> + Any(T &&value) : Any(std::in_place_type<T>, std::forward<T>(value)) + { + } + + ~Any() + { + info_->destruct(&buffer_); + } + + /** + * \note: Only needed because the template below does not count as copy assignment operator. + */ + Any &operator=(const Any &other) + { + if (this == &other) { + return *this; + } + this->~Any(); + new (this) Any(other); + return *this; + } + + /** Assign any value to the #Any. */ + template<typename T> Any &operator=(T &&other) + { + if constexpr (is_same_any_v<T>) { + if (this == &other) { + return *this; + } + } + this->~Any(); + new (this) Any(std::forward<T>(other)); + return *this; + } + + /** Destruct any existing value to make it empty. */ + void reset() + { + info_->destruct(&buffer_); + info_ = &Info::get_for_empty(); + } + + operator bool() const + { + return this->has_value(); + } + + bool has_value() const + { + return info_ != &Info::get_for_empty(); + } + + template<typename T, typename... Args> std::decay_t<T> &emplace(Args &&...args) + { + this->~Any(); + new (this) Any(std::in_place_type<T>, std::forward<Args>(args)...); + return this->get<T>(); + } + + /** Return true when the value that is currently stored is a #T. */ + template<typename T> bool is() const + { + return info_ == &this->template get_info<T>(); + } + + /** Get a pointer to the stored value. */ + void *get() + { + return const_cast<void *>(info_->get(&buffer_)); + } + + /** Get a pointer to the stored value. */ + const void *get() const + { + return info_->get(&buffer_); + } + + /** + * Get a reference to the stored value. This invokes undefined behavior when #T does not have the + * correct type. + */ + template<typename T> std::decay_t<T> &get() + { + BLI_assert(this->is<T>()); + return *static_cast<std::decay_t<T> *>(this->get()); + } + + /** + * Get a reference to the stored value. This invokes undefined behavior when #T does not have the + * correct type. + */ + template<typename T> const std::decay_t<T> &get() const + { + BLI_assert(this->is<T>()); + return *static_cast<const std::decay_t<T> *>(this->get()); + } + + /** + * Get extra information that has been stored for the contained type. + */ + const RealExtraInfo &extra_info() const + { + return info_->extra_info; + } +}; + +} // namespace blender |