src/tint/utils/rtti/castable.h - dawn - Git at Google

 // Copyright 2020 The Tint Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #ifndef SRC_TINT_UTILS_RTTI_CASTABLE_H_
 #define SRC_TINT_UTILS_RTTI_CASTABLE_H_

 #include <stdint.h>
 #include <functional>
 #include <tuple>
 #include <type_traits>
 #include <utility>

 #include "src/tint/utils/math/crc32.h"
 #include "src/tint/utils/traits/traits.h"

 #if defined(__clang__)
 /// Temporarily disable certain warnings when using Castable API
 #define TINT_CASTABLE_PUSH_DISABLE_WARNINGS()                                 \
     _Pragma("clang diagnostic push")                                     /**/ \
         _Pragma("clang diagnostic ignored \"-Wundefined-var-template\"") /**/ \
         static_assert(true, "require extra semicolon")

 /// Restore disabled warnings
 #define TINT_CASTABLE_POP_DISABLE_WARNINGS() \
     _Pragma("clang diagnostic pop") /**/     \
         static_assert(true, "require extra semicolon")
 #else
 #define TINT_CASTABLE_PUSH_DISABLE_WARNINGS() static_assert(true, "require extra semicolon")
 #define TINT_CASTABLE_POP_DISABLE_WARNINGS() static_assert(true, "require extra semicolon")
 #endif

 TINT_CASTABLE_PUSH_DISABLE_WARNINGS();

 // Forward declarations
 namespace tint {
 class CastableBase;

 /// Ignore is used as a special type used for skipping over types for trait
 /// helper functions.
 class Ignore {};
 }  // namespace tint

 namespace tint::detail {
 template <typename T>
 struct TypeInfoOf;
 }  // namespace tint::detail

 namespace tint {

 /// True if all template types that are not Ignore derive from CastableBase
 template <typename... TYPES>
 static constexpr bool IsCastable =
     ((tint::traits::IsTypeOrDerived<TYPES, CastableBase> || std::is_same_v<TYPES, Ignore>)&&...) &&
     !(std::is_same_v<TYPES, Ignore> && ...);

 /// Helper macro to instantiate the TypeInfo<T> template for `CLASS`.
 #define TINT_INSTANTIATE_TYPEINFO(CLASS)                        \
     TINT_CASTABLE_PUSH_DISABLE_WARNINGS();                      \
     template <>                                                 \
     const tint::TypeInfo tint::detail::TypeInfoOf<CLASS>::info{ \
         &tint::detail::TypeInfoOf<CLASS::TrueBase>::info,       \
         #CLASS,                                                 \
         tint::TypeInfo::HashCodeOf<CLASS>(),                    \
         tint::TypeInfo::FullHashCodeOf<CLASS>(),                \
     };                                                          \
     TINT_CASTABLE_POP_DISABLE_WARNINGS();                       \
     static_assert(std::is_same_v<CLASS, CLASS::Base::Class>,    \
                   #CLASS " does not derive from Castable<" #CLASS "[, BASE]>")

 /// Bit flags that can be passed to the template parameter `FLAGS` of Is() and As().
 enum CastFlags {
     /// Disables the static_assert() inside Is(), that compile-time-verifies that the cast is
     /// possible. This flag may be useful for highly-generic template
     /// code that needs to compile for template permutations that generate
     /// impossible casts.
     kDontErrorOnImpossibleCast = 1,
 };

 /// The type of a hash code
 using HashCode = uint64_t;

 /// Maybe checks to see if an object with the full hashcode @p object_full_hashcode could
 /// potentially be of, or derive from the type with the hashcode @p query_hashcode.
 /// @param type_hashcode the hashcode of the type
 /// @param object_full_hashcode the full hashcode of the object being queried
 /// @returns true if the object with the given full hashcode could be one of the template types.
 inline bool Maybe(HashCode type_hashcode, HashCode object_full_hashcode) {
     return (object_full_hashcode & type_hashcode) == type_hashcode;
 }

 /// MaybeAnyOf checks to see if an object with the full hashcode @p object_full_hashcode could
 /// potentially be of, or derive from the types with the combined hashcode @p combined_hashcode.
 /// @param combined_hashcode the bitwise OR'd hashcodes of the types
 /// @param object_full_hashcode the full hashcode of the object being queried
 /// @returns true if the object with the given full hashcode could be one of the template types.
 inline bool MaybeAnyOf(HashCode combined_hashcode, HashCode object_full_hashcode) {
     // Compare the object's hashcode to the bitwise-or of all the tested type's hashcodes. If
     // there's no intersection of bits in the two masks, then we can guarantee that the type is not
     // in `TO`.
     HashCode mask = object_full_hashcode & combined_hashcode;
     // HashCodeOf() ensures that two bits are always set for every hash, so we can quickly
     // eliminate the bitmask where only one bit is set.
     HashCode two_bits = mask & (mask - 1);
     return two_bits != 0;
 }

 /// TypeInfo holds type information for a Castable type.
 struct TypeInfo {
     /// The base class of this type
     const TypeInfo* base;
     /// The type name
     const char* name;
     /// The type hash code
     const HashCode hashcode;
     /// The type hash code bitwise-or'd with all ancestor's hashcodes.
     const HashCode full_hashcode;

     /// @returns true if `type` derives from the class `TO`
     /// @param object the object type to test from, which must be, or derive from type `FROM`.
     /// @see CastFlags
     template <typename TO, typename FROM, int FLAGS = 0>
     static inline bool Is(const tint::TypeInfo* object) {
         constexpr const bool downcast = std::is_base_of<FROM, TO>::value;
         constexpr const bool upcast = std::is_base_of<TO, FROM>::value;
         constexpr const bool nocast = std::is_same<FROM, TO>::value;
         constexpr const bool assert_is_castable = (FLAGS & kDontErrorOnImpossibleCast) == 0;

         static_assert(upcast || downcast || nocast || !assert_is_castable, "impossible cast");

         return upcast || nocast || object->Is<TO>();
     }

     /// @returns true if this type derives from the class `T`
     template <typename T>
     inline bool Is() const {
         auto* type = &Of<std::remove_cv_t<T>>();

         if constexpr (std::is_final_v<T>) {
             // T is final, so nothing can derive from T.
             // We do not need to check ancestors, only whether this type is equal to the type T.
             return type == this;
         } else {
             return Is(type);
         }
     }

     /// @param type the test type info
     /// @returns true if the class with this TypeInfo is of, or derives from the
     /// class with the given TypeInfo.
     inline bool Is(const tint::TypeInfo* type) const {
         if (!Maybe(type->hashcode, full_hashcode)) {
             return false;
         }

         // Walk the base types, starting with this TypeInfo, to see if any of the pointers match
         // `type`.
         for (auto* ti = this; ti != nullptr; ti = ti->base) {
             if (ti == type) {
                 return true;
             }
         }
         return false;
     }

     /// @returns the static TypeInfo for the type T
     template <typename T>
     static const TypeInfo& Of() {
         return tint::detail::TypeInfoOf<std::remove_cv_t<T>>::info;
     }

     /// @returns a compile-time hashcode for the type `T`.
     /// @note the returned hashcode will have exactly 2 bits set, as the hashes are expected to be
     /// used in bloom-filters which will quickly saturate when multiple hashcodes are bitwise-or'd
     /// together.
     template <typename T>
     static constexpr HashCode HashCodeOf() {
         static_assert(IsCastable<T>, "T is not Castable");
         static_assert(std::is_same_v<T, std::remove_cv_t<T>>,
                       "Strip const / volatile decorations before calling HashCodeOf");
         /// Use the compiler's "pretty" function name, which includes the template
         /// type, to obtain a unique hash value.
 #ifdef _MSC_VER
         constexpr uint32_t crc = tint::CRC32(__FUNCSIG__);
 #else
         constexpr uint32_t crc = tint::CRC32(__PRETTY_FUNCTION__);
 #endif
         constexpr uint32_t bit_a = (crc & 63);
         constexpr uint32_t bit_b = ((crc >> 6) & 63);
         constexpr uint32_t bit_c = (bit_a == bit_b) ? ((bit_a + 1) & 63) : bit_b;
         return (static_cast<HashCode>(1) << bit_a) | (static_cast<HashCode>(1) << bit_c);
     }

     /// @returns the hashcode of the given type, bitwise-or'd with the hashcodes of all base
     /// classes.
     template <typename T>
     static constexpr HashCode FullHashCodeOf() {
         if constexpr (std::is_same_v<T, CastableBase>) {
             return HashCodeOf<CastableBase>();
         } else {
             return HashCodeOf<T>() | FullHashCodeOf<typename T::TrueBase>();
         }
     }

     /// @returns the bitwise-or'd hashcodes of all the types of the tuple `TUPLE`.
     /// @see HashCodeOf
     template <typename TUPLE>
     static constexpr HashCode CombinedHashCodeOfTuple() {
         constexpr auto kCount = std::tuple_size_v<TUPLE>;
         if constexpr (kCount == 0) {
             return 0;
         } else if constexpr (kCount == 1) {
             return HashCodeOf<std::remove_cv_t<std::tuple_element_t<0, TUPLE>>>();
         } else {
             constexpr auto kMid = kCount / 2;
             return CombinedHashCodeOfTuple<tint::traits::SliceTuple<0, kMid, TUPLE>>() |
                    CombinedHashCodeOfTuple<tint::traits::SliceTuple<kMid, kCount - kMid, TUPLE>>();
         }
     }

     /// @returns the bitwise-or'd hashcodes of all the template parameter types.
     /// @see HashCodeOf
     template <typename... TYPES>
     static constexpr HashCode CombinedHashCodeOf() {
         return CombinedHashCodeOfTuple<std::tuple<TYPES...>>();
     }

     /// @returns true if this TypeInfo is of, or derives from any of the types in `TUPLE`.
     template <typename TUPLE>
     inline bool IsAnyOfTuple() const {
         constexpr auto kCount = std::tuple_size_v<TUPLE>;
         if constexpr (kCount == 0) {
             return false;
         } else if constexpr (kCount == 1) {
             return Is(&Of<std::tuple_element_t<0, TUPLE>>());
         } else {
             if (MaybeAnyOf(TypeInfo::CombinedHashCodeOfTuple<TUPLE>(), full_hashcode)) {
                 // Possibly one of the types in `TUPLE`.
                 // Split the search in two, and scan each block.
                 static constexpr auto kMid = kCount / 2;
                 return IsAnyOfTuple<tint::traits::SliceTuple<0, kMid, TUPLE>>() ||
                        IsAnyOfTuple<tint::traits::SliceTuple<kMid, kCount - kMid, TUPLE>>();
             }
             return false;
         }
     }

     /// @returns true if this TypeInfo is of, or derives from any of the types in `TYPES`.
     template <typename... TYPES>
     inline bool IsAnyOf() const {
         return IsAnyOfTuple<std::tuple<TYPES...>>();
     }
 };

 namespace detail {

 /// TypeInfoOf contains a single TypeInfo field for the type T.
 /// TINT_INSTANTIATE_TYPEINFO() must be defined in a .cpp file for each type `T`.
 template <typename T>
 struct TypeInfoOf {
     /// The unique TypeInfo for the type T.
     static const TypeInfo info;
 };

 /// A placeholder structure used for template parameters that need a default type, but can always be
 /// automatically inferred.
 struct Infer;

 }  // namespace detail

 /// @returns true if `obj` is a valid pointer, and is of, or derives from the class `TO`
 /// @param obj the object to test from
 /// @see CastFlags
 template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
 inline bool Is(FROM* obj) {
     if (obj == nullptr) {
         return false;
     }
     return TypeInfo::Is<TO, FROM, FLAGS>(&obj->TypeInfo());
 }

 /// @returns true if `obj` is a valid pointer, and is of, or derives from the type `TYPE`, and
 /// pred(const TYPE*) returns true
 /// @param obj the object to test from
 /// @param pred predicate function with signature `bool(const TYPE*)` called iff object is of, or
 /// derives from the class `TYPE`.
 /// @see CastFlags
 template <typename TYPE,
           int FLAGS = 0,
           typename OBJ = tint::detail::Infer,
           typename Pred = tint::detail::Infer>
 inline bool Is(OBJ* obj, Pred&& pred) {
     return Is<TYPE, FLAGS, OBJ>(obj) && pred(static_cast<std::add_const_t<TYPE>*>(obj));
 }

 /// @returns true if `obj` is a valid pointer, and is of, or derives from any of the types in
 /// `TYPES`.
 /// @param obj the object to query.
 template <typename... TYPES, typename OBJ>
 inline bool IsAnyOf(OBJ* obj) {
     if (!obj) {
         return false;
     }
     return obj->TypeInfo().template IsAnyOf<TYPES...>();
 }

 /// @returns obj dynamically cast to the type `TO` or `nullptr` if this object does not derive from
 /// `TO`.
 /// @param obj the object to cast from
 /// @see CastFlags
 template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
 inline TO* As(FROM* obj) {
     auto* as_castable = static_cast<CastableBase*>(obj);
     return Is<TO, FLAGS>(obj) ? static_cast<TO*>(as_castable) : nullptr;
 }

 /// @returns obj dynamically cast to the type `TO` or `nullptr` if this object does not derive from
 /// `TO`.
 /// @param obj the object to cast from
 /// @see CastFlags
 template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
 inline const TO* As(const FROM* obj) {
     auto* as_castable = static_cast<const CastableBase*>(obj);
     return Is<TO, FLAGS>(obj) ? static_cast<const TO*>(as_castable) : nullptr;
 }

 /// CastableBase is the base class for all Castable objects.
 /// It is not encouraged to directly derive from CastableBase without using the Castable helper
 /// template.
 /// @see Castable
 class CastableBase {
   public:
     /// Copy constructor
     CastableBase(const CastableBase&);

     /// Destructor
     virtual ~CastableBase();

     /// Copy assignment
     /// @param other the CastableBase to copy
     /// @returns the new CastableBase
     CastableBase& operator=(const CastableBase& other) = default;

     /// @returns the TypeInfo of the object
     inline const tint::TypeInfo& TypeInfo() const { return *type_info_; }

     /// @returns true if this object is of, or derives from the class `TO`
     template <typename TO>
     inline bool Is() const {
         return tint::Is<TO>(this);
     }

     /// @returns true if this object is of, or derives from the class `TO` and pred(const TO*)
     /// returns true
     /// @param pred predicate function with signature `bool(const TO*)` called iff object is of, or
     /// derives from the class `TO`.
     template <typename TO, int FLAGS = 0, typename Pred = tint::detail::Infer>
     inline bool Is(Pred&& pred) const {
         return tint::Is<TO, FLAGS>(this, std::forward<Pred>(pred));
     }

     /// @returns true if this object is of, or derives from any of the `TO` classes.
     template <typename... TO>
     inline bool IsAnyOf() const {
         return tint::IsAnyOf<TO...>(this);
     }

     /// @returns this object dynamically cast to the type `TO` or `nullptr` if this object does not
     /// derive from `TO`.
     /// @see CastFlags
     template <typename TO, int FLAGS = 0>
     inline TO* As() {
         return tint::As<TO, FLAGS>(this);
     }

     /// @returns this object dynamically cast to the type `TO` or `nullptr` if this object does not
     /// derive from `TO`.
     /// @see CastFlags
     template <typename TO, int FLAGS = 0>
     inline const TO* As() const {
         return tint::As<const TO, FLAGS>(this);
     }

   protected:
     CastableBase() = default;

     /// The type information for the object
     const tint::TypeInfo* type_info_ = nullptr;
 };

 /// Castable is a helper to derive `CLASS` from `BASE`, automatically implementing the Is() and As()
 /// methods, along with a #Base type alias.
 ///
 /// Example usage:
 ///
 /// ```
 /// class Animal : public Castable<Animal> {};
 ///
 /// class Sheep : public Castable<Sheep, Animal> {};
 ///
 /// Sheep* cast_to_sheep(Animal* animal) {
 ///    // You can query whether a Castable is of the given type with Is<T>():
 ///    printf("animal is a sheep? %s", animal->Is<Sheep>() ? "yes" : "no");
 ///
 ///    // You can always just try the cast with As<T>().
 ///    // If the object is not of the correct type, As<T>() will return nullptr:
 ///    return animal->As<Sheep>();
 /// }
 /// ```
 template <typename CLASS, typename BASE = CastableBase>
 class Castable : public BASE {
   public:
     /// A type alias to this Castable. Commonly used in derived type constructors to forward
     /// constructor arguments to BASE.
     using Base = Castable;

     /// A type alias for `BASE`.
     using TrueBase = BASE;

     /// A type alias for `CLASS`.
     using Class = CLASS;

     /// Constructor
     /// @param arguments the arguments to forward to the base class.
     template <typename... ARGS>
     inline explicit Castable(ARGS&&... arguments) : TrueBase(std::forward<ARGS>(arguments)...) {
         this->type_info_ = &TypeInfo::Of<CLASS>();
     }

     /// @returns true if this object is of, or derives from the class `TO`
     /// @see CastFlags
     template <typename TO, int FLAGS = 0>
     inline bool Is() const {
         return tint::Is<TO, FLAGS>(static_cast<const CLASS*>(this));
     }

     /// @returns true if this object is of, or derives from the class `TO` and
     /// pred(const TO*) returns true
     /// @param pred predicate function with signature `bool(const TO*)` called iff
     /// object is of, or derives from the class `TO`.
     template <int FLAGS = 0, typename Pred = tint::detail::Infer>
     inline bool Is(Pred&& pred) const {
         using TO = typename std::remove_pointer<tint::traits::ParameterType<Pred, 0>>::type;
         return tint::Is<TO, FLAGS>(static_cast<const CLASS*>(this), std::forward<Pred>(pred));
     }

     /// @returns true if this object is of, or derives from any of the `TO`
     /// classes.
     template <typename... TO>
     inline bool IsAnyOf() const {
         return tint::IsAnyOf<TO...>(static_cast<const CLASS*>(this));
     }

     /// @returns this object dynamically cast to the type `TO` or `nullptr` if
     /// this object does not derive from `TO`.
     /// @see CastFlags
     template <typename TO, int FLAGS = 0>
     inline TO* As() {
         return tint::As<TO, FLAGS>(this);
     }

     /// @returns this object dynamically cast to the type `TO` or `nullptr` if
     /// this object does not derive from `TO`.
     /// @see CastFlags
     template <typename TO, int FLAGS = 0>
     inline const TO* As() const {
         return tint::As<const TO, FLAGS>(this);
     }
 };

 namespace detail {
 /// <code>typename CastableCommonBaseImpl<TYPES>::type</code> resolves to the common base class for
 /// all of TYPES.
 template <typename... TYPES>
 struct CastableCommonBaseImpl {};

 /// Alias to typename CastableCommonBaseImpl<TYPES>::type
 template <typename... TYPES>
 using CastableCommonBase = typename CastableCommonBaseImpl<TYPES...>::type;

 /// CastableCommonBaseImpl template specialization for a single type
 template <typename T>
 struct CastableCommonBaseImpl<T> {
     /// Common base class of a single type is itself
     using type = T;
 };

 /// CastableCommonBaseImpl A <-> CastableBase specialization
 template <typename A>
 struct CastableCommonBaseImpl<A, CastableBase> {
     /// Common base class for A and CastableBase is CastableBase
     using type = CastableBase;
 };

 /// CastableCommonBaseImpl T <-> Ignore specialization
 template <typename T>
 struct CastableCommonBaseImpl<T, Ignore> {
     /// Resolves to T as the other type is ignored
     using type = T;
 };

 /// CastableCommonBaseImpl Ignore <-> T specialization
 template <typename T>
 struct CastableCommonBaseImpl<Ignore, T> {
     /// Resolves to T as the other type is ignored
     using type = T;
 };

 /// CastableCommonBaseImpl A <-> B specialization
 template <typename A, typename B>
 struct CastableCommonBaseImpl<A, B> {
     /// The common base class for A, B and OTHERS
     using type = std::conditional_t<tint::traits::IsTypeOrDerived<A, B>,
                                     B,  // A derives from B
                                     CastableCommonBase<A, typename B::TrueBase>>;
 };

 /// CastableCommonBaseImpl 3+ types specialization
 template <typename A, typename B, typename... OTHERS>
 struct CastableCommonBaseImpl<A, B, OTHERS...> {
     /// The common base class for A, B and OTHERS
     using type = CastableCommonBase<CastableCommonBase<A, B>, OTHERS...>;
 };

 }  // namespace detail

 /// Resolves to the common most derived type that each of the types in `TYPES` derives from.
 template <typename... TYPES>
 using CastableCommonBase = tint::detail::CastableCommonBase<TYPES...>;

 }  // namespace tint

 namespace tint {

 using tint::As;
 using tint::Is;

 }  // namespace tint

 TINT_CASTABLE_POP_DISABLE_WARNINGS();

 #endif  // SRC_TINT_UTILS_RTTI_CASTABLE_H_
	// Copyright 2020 The Tint Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#ifndef SRC_TINT_UTILS_RTTI_CASTABLE_H_
	#define SRC_TINT_UTILS_RTTI_CASTABLE_H_

	#include <stdint.h>
	#include <functional>
	#include <tuple>
	#include <type_traits>
	#include <utility>

	#include "src/tint/utils/math/crc32.h"
	#include "src/tint/utils/traits/traits.h"

	#if defined(__clang__)
	/// Temporarily disable certain warnings when using Castable API
	#define TINT_CASTABLE_PUSH_DISABLE_WARNINGS() \
	_Pragma("clang diagnostic push") /**/ \
	_Pragma("clang diagnostic ignored \"-Wundefined-var-template\"") /**/ \
	static_assert(true, "require extra semicolon")

	/// Restore disabled warnings
	#define TINT_CASTABLE_POP_DISABLE_WARNINGS() \
	_Pragma("clang diagnostic pop") /**/ \
	static_assert(true, "require extra semicolon")
	#else
	#define TINT_CASTABLE_PUSH_DISABLE_WARNINGS() static_assert(true, "require extra semicolon")
	#define TINT_CASTABLE_POP_DISABLE_WARNINGS() static_assert(true, "require extra semicolon")
	#endif

	TINT_CASTABLE_PUSH_DISABLE_WARNINGS();

	// Forward declarations
	namespace tint {
	class CastableBase;

	/// Ignore is used as a special type used for skipping over types for trait
	/// helper functions.
	class Ignore {};
	} // namespace tint

	namespace tint::detail {
	template <typename T>
	struct TypeInfoOf;
	} // namespace tint::detail

	namespace tint {

	/// True if all template types that are not Ignore derive from CastableBase
	template <typename... TYPES>
	static constexpr bool IsCastable =
	((tint::traits::IsTypeOrDerived<TYPES, CastableBase> \|\| std::is_same_v<TYPES, Ignore>)&&...) &&
	!(std::is_same_v<TYPES, Ignore> && ...);

	/// Helper macro to instantiate the TypeInfo<T> template for `CLASS`.
	#define TINT_INSTANTIATE_TYPEINFO(CLASS) \
	TINT_CASTABLE_PUSH_DISABLE_WARNINGS(); \
	template <> \
	const tint::TypeInfo tint::detail::TypeInfoOf<CLASS>::info{ \
	&tint::detail::TypeInfoOf<CLASS::TrueBase>::info, \
	#CLASS, \
	tint::TypeInfo::HashCodeOf<CLASS>(), \
	tint::TypeInfo::FullHashCodeOf<CLASS>(), \
	}; \
	TINT_CASTABLE_POP_DISABLE_WARNINGS(); \
	static_assert(std::is_same_v<CLASS, CLASS::Base::Class>, \
	#CLASS " does not derive from Castable<" #CLASS "[, BASE]>")

	/// Bit flags that can be passed to the template parameter `FLAGS` of Is() and As().
	enum CastFlags {
	/// Disables the static_assert() inside Is(), that compile-time-verifies that the cast is
	/// possible. This flag may be useful for highly-generic template
	/// code that needs to compile for template permutations that generate
	/// impossible casts.
	kDontErrorOnImpossibleCast = 1,
	};

	/// The type of a hash code
	using HashCode = uint64_t;

	/// Maybe checks to see if an object with the full hashcode @p object_full_hashcode could
	/// potentially be of, or derive from the type with the hashcode @p query_hashcode.
	/// @param type_hashcode the hashcode of the type
	/// @param object_full_hashcode the full hashcode of the object being queried
	/// @returns true if the object with the given full hashcode could be one of the template types.
	inline bool Maybe(HashCode type_hashcode, HashCode object_full_hashcode) {
	return (object_full_hashcode & type_hashcode) == type_hashcode;
	}

	/// MaybeAnyOf checks to see if an object with the full hashcode @p object_full_hashcode could
	/// potentially be of, or derive from the types with the combined hashcode @p combined_hashcode.
	/// @param combined_hashcode the bitwise OR'd hashcodes of the types
	/// @param object_full_hashcode the full hashcode of the object being queried
	/// @returns true if the object with the given full hashcode could be one of the template types.
	inline bool MaybeAnyOf(HashCode combined_hashcode, HashCode object_full_hashcode) {
	// Compare the object's hashcode to the bitwise-or of all the tested type's hashcodes. If
	// there's no intersection of bits in the two masks, then we can guarantee that the type is not
	// in `TO`.
	HashCode mask = object_full_hashcode & combined_hashcode;
	// HashCodeOf() ensures that two bits are always set for every hash, so we can quickly
	// eliminate the bitmask where only one bit is set.
	HashCode two_bits = mask & (mask - 1);
	return two_bits != 0;
	}

	/// TypeInfo holds type information for a Castable type.
	struct TypeInfo {
	/// The base class of this type
	const TypeInfo* base;
	/// The type name
	const char* name;
	/// The type hash code
	const HashCode hashcode;
	/// The type hash code bitwise-or'd with all ancestor's hashcodes.
	const HashCode full_hashcode;

	/// @returns true if `type` derives from the class `TO`
	/// @param object the object type to test from, which must be, or derive from type `FROM`.
	/// @see CastFlags
	template <typename TO, typename FROM, int FLAGS = 0>
	static inline bool Is(const tint::TypeInfo* object) {
	constexpr const bool downcast = std::is_base_of<FROM, TO>::value;
	constexpr const bool upcast = std::is_base_of<TO, FROM>::value;
	constexpr const bool nocast = std::is_same<FROM, TO>::value;
	constexpr const bool assert_is_castable = (FLAGS & kDontErrorOnImpossibleCast) == 0;

	static_assert(upcast \|\| downcast \|\| nocast \|\| !assert_is_castable, "impossible cast");

	return upcast \|\| nocast \|\| object->Is<TO>();
	}

	/// @returns true if this type derives from the class `T`
	template <typename T>
	inline bool Is() const {
	auto* type = &Of<std::remove_cv_t<T>>();

	if constexpr (std::is_final_v<T>) {
	// T is final, so nothing can derive from T.
	// We do not need to check ancestors, only whether this type is equal to the type T.
	return type == this;
	} else {
	return Is(type);
	}
	}

	/// @param type the test type info
	/// @returns true if the class with this TypeInfo is of, or derives from the
	/// class with the given TypeInfo.
	inline bool Is(const tint::TypeInfo* type) const {
	if (!Maybe(type->hashcode, full_hashcode)) {
	return false;
	}

	// Walk the base types, starting with this TypeInfo, to see if any of the pointers match
	// `type`.
	for (auto* ti = this; ti != nullptr; ti = ti->base) {
	if (ti == type) {
	return true;
	}
	}
	return false;
	}

	/// @returns the static TypeInfo for the type T
	template <typename T>
	static const TypeInfo& Of() {
	return tint::detail::TypeInfoOf<std::remove_cv_t<T>>::info;
	}

	/// @returns a compile-time hashcode for the type `T`.
	/// @note the returned hashcode will have exactly 2 bits set, as the hashes are expected to be
	/// used in bloom-filters which will quickly saturate when multiple hashcodes are bitwise-or'd
	/// together.
	template <typename T>
	static constexpr HashCode HashCodeOf() {
	static_assert(IsCastable<T>, "T is not Castable");
	static_assert(std::is_same_v<T, std::remove_cv_t<T>>,
	"Strip const / volatile decorations before calling HashCodeOf");
	/// Use the compiler's "pretty" function name, which includes the template
	/// type, to obtain a unique hash value.
	#ifdef _MSC_VER
	constexpr uint32_t crc = tint::CRC32(__FUNCSIG__);
	#else
	constexpr uint32_t crc = tint::CRC32(__PRETTY_FUNCTION__);
	#endif
	constexpr uint32_t bit_a = (crc & 63);
	constexpr uint32_t bit_b = ((crc >> 6) & 63);
	constexpr uint32_t bit_c = (bit_a == bit_b) ? ((bit_a + 1) & 63) : bit_b;
	return (static_cast<HashCode>(1) << bit_a) \| (static_cast<HashCode>(1) << bit_c);
	}

	/// @returns the hashcode of the given type, bitwise-or'd with the hashcodes of all base
	/// classes.
	template <typename T>
	static constexpr HashCode FullHashCodeOf() {
	if constexpr (std::is_same_v<T, CastableBase>) {
	return HashCodeOf<CastableBase>();
	} else {
	return HashCodeOf<T>() \| FullHashCodeOf<typename T::TrueBase>();
	}
	}

	/// @returns the bitwise-or'd hashcodes of all the types of the tuple `TUPLE`.
	/// @see HashCodeOf
	template <typename TUPLE>
	static constexpr HashCode CombinedHashCodeOfTuple() {
	constexpr auto kCount = std::tuple_size_v<TUPLE>;
	if constexpr (kCount == 0) {
	return 0;
	} else if constexpr (kCount == 1) {
	return HashCodeOf<std::remove_cv_t<std::tuple_element_t<0, TUPLE>>>();
	} else {
	constexpr auto kMid = kCount / 2;
	return CombinedHashCodeOfTuple<tint::traits::SliceTuple<0, kMid, TUPLE>>() \|
	CombinedHashCodeOfTuple<tint::traits::SliceTuple<kMid, kCount - kMid, TUPLE>>();
	}
	}

	/// @returns the bitwise-or'd hashcodes of all the template parameter types.
	/// @see HashCodeOf
	template <typename... TYPES>
	static constexpr HashCode CombinedHashCodeOf() {
	return CombinedHashCodeOfTuple<std::tuple<TYPES...>>();
	}

	/// @returns true if this TypeInfo is of, or derives from any of the types in `TUPLE`.
	template <typename TUPLE>
	inline bool IsAnyOfTuple() const {
	constexpr auto kCount = std::tuple_size_v<TUPLE>;
	if constexpr (kCount == 0) {
	return false;
	} else if constexpr (kCount == 1) {
	return Is(&Of<std::tuple_element_t<0, TUPLE>>());
	} else {
	if (MaybeAnyOf(TypeInfo::CombinedHashCodeOfTuple<TUPLE>(), full_hashcode)) {
	// Possibly one of the types in `TUPLE`.
	// Split the search in two, and scan each block.
	static constexpr auto kMid = kCount / 2;
	return IsAnyOfTuple<tint::traits::SliceTuple<0, kMid, TUPLE>>() \|\|
	IsAnyOfTuple<tint::traits::SliceTuple<kMid, kCount - kMid, TUPLE>>();
	}
	return false;
	}
	}

	/// @returns true if this TypeInfo is of, or derives from any of the types in `TYPES`.
	template <typename... TYPES>
	inline bool IsAnyOf() const {
	return IsAnyOfTuple<std::tuple<TYPES...>>();
	}
	};

	namespace detail {

	/// TypeInfoOf contains a single TypeInfo field for the type T.
	/// TINT_INSTANTIATE_TYPEINFO() must be defined in a .cpp file for each type `T`.
	template <typename T>
	struct TypeInfoOf {
	/// The unique TypeInfo for the type T.
	static const TypeInfo info;
	};

	/// A placeholder structure used for template parameters that need a default type, but can always be
	/// automatically inferred.
	struct Infer;

	} // namespace detail

	/// @returns true if `obj` is a valid pointer, and is of, or derives from the class `TO`
	/// @param obj the object to test from
	/// @see CastFlags
	template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
	inline bool Is(FROM* obj) {
	if (obj == nullptr) {
	return false;
	}
	return TypeInfo::Is<TO, FROM, FLAGS>(&obj->TypeInfo());
	}

	/// @returns true if `obj` is a valid pointer, and is of, or derives from the type `TYPE`, and
	/// pred(const TYPE*) returns true
	/// @param obj the object to test from
	/// @param pred predicate function with signature `bool(const TYPE*)` called iff object is of, or
	/// derives from the class `TYPE`.
	/// @see CastFlags
	template <typename TYPE,
	int FLAGS = 0,
	typename OBJ = tint::detail::Infer,
	typename Pred = tint::detail::Infer>
	inline bool Is(OBJ* obj, Pred&& pred) {
	return Is<TYPE, FLAGS, OBJ>(obj) && pred(static_cast<std::add_const_t<TYPE>*>(obj));
	}

	/// @returns true if `obj` is a valid pointer, and is of, or derives from any of the types in
	/// `TYPES`.
	/// @param obj the object to query.
	template <typename... TYPES, typename OBJ>
	inline bool IsAnyOf(OBJ* obj) {
	if (!obj) {
	return false;
	}
	return obj->TypeInfo().template IsAnyOf<TYPES...>();
	}

	/// @returns obj dynamically cast to the type `TO` or `nullptr` if this object does not derive from
	/// `TO`.
	/// @param obj the object to cast from
	/// @see CastFlags
	template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
	inline TO* As(FROM* obj) {
	auto* as_castable = static_cast<CastableBase*>(obj);
	return Is<TO, FLAGS>(obj) ? static_cast<TO*>(as_castable) : nullptr;
	}

	/// @returns obj dynamically cast to the type `TO` or `nullptr` if this object does not derive from
	/// `TO`.
	/// @param obj the object to cast from
	/// @see CastFlags
	template <typename TO, int FLAGS = 0, typename FROM = tint::detail::Infer>
	inline const TO* As(const FROM* obj) {
	auto* as_castable = static_cast<const CastableBase*>(obj);
	return Is<TO, FLAGS>(obj) ? static_cast<const TO*>(as_castable) : nullptr;
	}

	/// CastableBase is the base class for all Castable objects.
	/// It is not encouraged to directly derive from CastableBase without using the Castable helper
	/// template.
	/// @see Castable
	class CastableBase {
	public:
	/// Copy constructor
	CastableBase(const CastableBase&);

	/// Destructor
	virtual ~CastableBase();

	/// Copy assignment
	/// @param other the CastableBase to copy
	/// @returns the new CastableBase
	CastableBase& operator=(const CastableBase& other) = default;

	/// @returns the TypeInfo of the object
	inline const tint::TypeInfo& TypeInfo() const { return *type_info_; }

	/// @returns true if this object is of, or derives from the class `TO`
	template <typename TO>
	inline bool Is() const {
	return tint::Is<TO>(this);
	}

	/// @returns true if this object is of, or derives from the class `TO` and pred(const TO*)
	/// returns true
	/// @param pred predicate function with signature `bool(const TO*)` called iff object is of, or
	/// derives from the class `TO`.
	template <typename TO, int FLAGS = 0, typename Pred = tint::detail::Infer>
	inline bool Is(Pred&& pred) const {
	return tint::Is<TO, FLAGS>(this, std::forward<Pred>(pred));
	}

	/// @returns true if this object is of, or derives from any of the `TO` classes.
	template <typename... TO>
	inline bool IsAnyOf() const {
	return tint::IsAnyOf<TO...>(this);
	}

	/// @returns this object dynamically cast to the type `TO` or `nullptr` if this object does not
	/// derive from `TO`.
	/// @see CastFlags
	template <typename TO, int FLAGS = 0>
	inline TO* As() {
	return tint::As<TO, FLAGS>(this);
	}

	/// @returns this object dynamically cast to the type `TO` or `nullptr` if this object does not
	/// derive from `TO`.
	/// @see CastFlags
	template <typename TO, int FLAGS = 0>
	inline const TO* As() const {
	return tint::As<const TO, FLAGS>(this);
	}

	protected:
	CastableBase() = default;

	/// The type information for the object
	const tint::TypeInfo* type_info_ = nullptr;
	};

	/// Castable is a helper to derive `CLASS` from `BASE`, automatically implementing the Is() and As()
	/// methods, along with a #Base type alias.
	///
	/// Example usage:
	///
	/// ```
	/// class Animal : public Castable<Animal> {};
	///
	/// class Sheep : public Castable<Sheep, Animal> {};
	///
	/// Sheep* cast_to_sheep(Animal* animal) {
	/// // You can query whether a Castable is of the given type with Is<T>():
	/// printf("animal is a sheep? %s", animal->Is<Sheep>() ? "yes" : "no");
	///
	/// // You can always just try the cast with As<T>().
	/// // If the object is not of the correct type, As<T>() will return nullptr:
	/// return animal->As<Sheep>();
	/// }
	/// ```
	template <typename CLASS, typename BASE = CastableBase>
	class Castable : public BASE {
	public:
	/// A type alias to this Castable. Commonly used in derived type constructors to forward
	/// constructor arguments to BASE.
	using Base = Castable;

	/// A type alias for `BASE`.
	using TrueBase = BASE;

	/// A type alias for `CLASS`.
	using Class = CLASS;

	/// Constructor
	/// @param arguments the arguments to forward to the base class.
	template <typename... ARGS>
	inline explicit Castable(ARGS&&... arguments) : TrueBase(std::forward<ARGS>(arguments)...) {
	this->type_info_ = &TypeInfo::Of<CLASS>();
	}

	/// @returns true if this object is of, or derives from the class `TO`
	/// @see CastFlags
	template <typename TO, int FLAGS = 0>
	inline bool Is() const {
	return tint::Is<TO, FLAGS>(static_cast<const CLASS*>(this));
	}

	/// @returns true if this object is of, or derives from the class `TO` and
	/// pred(const TO*) returns true
	/// @param pred predicate function with signature `bool(const TO*)` called iff
	/// object is of, or derives from the class `TO`.
	template <int FLAGS = 0, typename Pred = tint::detail::Infer>
	inline bool Is(Pred&& pred) const {
	using TO = typename std::remove_pointer<tint::traits::ParameterType<Pred, 0>>::type;
	return tint::Is<TO, FLAGS>(static_cast<const CLASS*>(this), std::forward<Pred>(pred));
	}

	/// @returns true if this object is of, or derives from any of the `TO`
	/// classes.
	template <typename... TO>
	inline bool IsAnyOf() const {
	return tint::IsAnyOf<TO...>(static_cast<const CLASS*>(this));
	}

	/// @returns this object dynamically cast to the type `TO` or `nullptr` if
	/// this object does not derive from `TO`.
	/// @see CastFlags
	template <typename TO, int FLAGS = 0>
	inline TO* As() {
	return tint::As<TO, FLAGS>(this);
	}

	/// @returns this object dynamically cast to the type `TO` or `nullptr` if
	/// this object does not derive from `TO`.
	/// @see CastFlags
	template <typename TO, int FLAGS = 0>
	inline const TO* As() const {
	return tint::As<const TO, FLAGS>(this);
	}
	};

	namespace detail {
	/// <code>typename CastableCommonBaseImpl<TYPES>::type</code> resolves to the common base class for
	/// all of TYPES.
	template <typename... TYPES>
	struct CastableCommonBaseImpl {};

	/// Alias to typename CastableCommonBaseImpl<TYPES>::type
	template <typename... TYPES>
	using CastableCommonBase = typename CastableCommonBaseImpl<TYPES...>::type;

	/// CastableCommonBaseImpl template specialization for a single type
	template <typename T>
	struct CastableCommonBaseImpl<T> {
	/// Common base class of a single type is itself
	using type = T;
	};

	/// CastableCommonBaseImpl A <-> CastableBase specialization
	template <typename A>
	struct CastableCommonBaseImpl<A, CastableBase> {
	/// Common base class for A and CastableBase is CastableBase
	using type = CastableBase;
	};

	/// CastableCommonBaseImpl T <-> Ignore specialization
	template <typename T>
	struct CastableCommonBaseImpl<T, Ignore> {
	/// Resolves to T as the other type is ignored
	using type = T;
	};

	/// CastableCommonBaseImpl Ignore <-> T specialization
	template <typename T>
	struct CastableCommonBaseImpl<Ignore, T> {
	/// Resolves to T as the other type is ignored
	using type = T;
	};

	/// CastableCommonBaseImpl A <-> B specialization
	template <typename A, typename B>
	struct CastableCommonBaseImpl<A, B> {
	/// The common base class for A, B and OTHERS
	using type = std::conditional_t<tint::traits::IsTypeOrDerived<A, B>,
	B, // A derives from B
	CastableCommonBase<A, typename B::TrueBase>>;
	};

	/// CastableCommonBaseImpl 3+ types specialization
	template <typename A, typename B, typename... OTHERS>
	struct CastableCommonBaseImpl<A, B, OTHERS...> {
	/// The common base class for A, B and OTHERS
	using type = CastableCommonBase<CastableCommonBase<A, B>, OTHERS...>;
	};

	} // namespace detail

	/// Resolves to the common most derived type that each of the types in `TYPES` derives from.
	template <typename... TYPES>
	using CastableCommonBase = tint::detail::CastableCommonBase<TYPES...>;

	} // namespace tint

	namespace tint {

	using tint::As;
	using tint::Is;

	} // namespace tint

	TINT_CASTABLE_POP_DISABLE_WARNINGS();

	#endif // SRC_TINT_UTILS_RTTI_CASTABLE_H_