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// 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_CASTABLE_H_
#define SRC_TINT_CASTABLE_H_
#include <stdint.h>
#include <functional>
#include <tuple>
#include <utility>
#include "src/tint/traits.h"
#include "src/tint/utils/bitcast.h"
#include "src/tint/utils/crc32.h"
#include "src/tint/utils/defer.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 =
((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()
/// 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,
};
/// TypeInfo holds type information for a Castable type.
struct TypeInfo {
/// The type of a hash code
using HashCode = uint64_t;
/// 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 {
// Optimization: Check whether the all the bits of the type's hashcode can
// be found in the full_hashcode. If a single bit is missing, then we
// can quickly tell that that this TypeInfo does not derive from `type`.
if ((full_hashcode & type->hashcode) != type->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 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 = utils::CRC32(__FUNCSIG__);
#else
constexpr uint32_t crc = utils::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<traits::SliceTuple<0, kMid, TUPLE>>() |
CombinedHashCodeOfTuple<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 {
// Optimization: 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 = full_hashcode & TypeInfo::CombinedHashCodeOfTuple<TUPLE>();
// 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);
if (two_bits) {
// Possibly one of the types in `TUPLE`.
// Split the search in two, and scan each block.
static constexpr auto kMid = kCount / 2;
return IsAnyOfTuple<traits::SliceTuple<0, kMid, TUPLE>>() ||
IsAnyOfTuple<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 = 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 = detail::Infer, typename Pred = 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`.OBJ
/// @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 = 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 = 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
virtual const tint::TypeInfo& TypeInfo() const = 0;
/// @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 = 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;
};
/// 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:
// Inherit the `BASE` class constructors.
using BASE::BASE;
/// A type alias for `CLASS` to easily access the `BASE` class members.
/// Base actually aliases to the Castable instead of `BASE` so that you can
/// use Base in the `CLASS` constructor.
using Base = Castable;
/// A type alias for `BASE`.
using TrueBase = BASE;
/// @returns the TypeInfo of the object
const tint::TypeInfo& TypeInfo() const override { return 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 = detail::Infer>
inline bool Is(Pred&& pred) const {
using TO = typename std::remove_pointer<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<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 = detail::CastableCommonBase<TYPES...>;
/// Default can be used as the default case for a Switch(), when all previous
/// cases failed to match.
///
/// Example:
/// ```
/// Switch(object,
/// [&](TypeA*) { /* ... */ },
/// [&](TypeB*) { /* ... */ },
/// [&](Default) { /* If not TypeA or TypeB */ });
/// ```
struct Default {};
namespace detail {
/// Evaluates to the Switch case type being matched by the switch case function
/// `FN`.
/// @note does not handle the Default case
/// @see Switch().
template <typename FN>
using SwitchCaseType = std::remove_pointer_t<traits::ParameterType<std::remove_reference_t<FN>, 0>>;
/// Evaluates to true if the function `FN` has the signature of a Default case
/// in a Switch().
/// @see Switch().
template <typename FN>
inline constexpr bool IsDefaultCase =
std::is_same_v<traits::ParameterType<std::remove_reference_t<FN>, 0>, Default>;
/// Searches the list of Switch cases for a Default case, returning the index of
/// the Default case. If the a Default case is not found in the tuple, then -1
/// is returned.
template <typename TUPLE, std::size_t START_IDX = 0>
constexpr int IndexOfDefaultCase() {
if constexpr (START_IDX < std::tuple_size_v<TUPLE>) {
return IsDefaultCase<std::tuple_element_t<START_IDX, TUPLE>>
? static_cast<int>(START_IDX)
: IndexOfDefaultCase<TUPLE, START_IDX + 1>();
} else {
return -1;
}
}
/// The implementation of Switch() for non-Default cases.
/// Switch splits the cases into two a low and high block of cases, and quickly
/// rules out blocks that cannot match by comparing the TypeInfo::HashCode of
/// the object and the cases in the block. If a block of cases may match the
/// given object's type, then that block is split into two, and the process
/// recurses. When NonDefaultCases() is called with a single case, then As<>
/// will be used to dynamically cast to the case type and if the cast succeeds,
/// then the case handler is called.
/// @returns true if a case handler was found, otherwise false.
template <typename T, typename RETURN_TYPE, typename... CASES>
inline bool NonDefaultCases(T* object,
const TypeInfo* type,
RETURN_TYPE* result,
std::tuple<CASES...>&& cases) {
using Cases = std::tuple<CASES...>;
(void)result; // Not always used, avoid warning.
static constexpr bool kHasReturnType = !std::is_same_v<RETURN_TYPE, void>;
static constexpr size_t kNumCases = sizeof...(CASES);
if constexpr (kNumCases == 0) {
// No cases. Nothing to do.
return false;
} else if constexpr (kNumCases == 1) { // NOLINT: cpplint doesn't understand
// `else if constexpr`
// Single case.
using CaseFunc = std::tuple_element_t<0, Cases>;
static_assert(!IsDefaultCase<CaseFunc>, "NonDefaultCases called with a Default case");
// Attempt to dynamically cast the object to the handler type. If that
// succeeds, call the case handler with the cast object.
using CaseType = SwitchCaseType<CaseFunc>;
if (type->Is<CaseType>()) {
auto* ptr = static_cast<CaseType*>(object);
if constexpr (kHasReturnType) {
new (result) RETURN_TYPE(static_cast<RETURN_TYPE>(std::get<0>(cases)(ptr)));
} else {
std::get<0>(cases)(ptr);
}
return true;
}
return false;
} else {
// Multiple cases.
// Check the hashcode bits to see if there's any possibility of a case matching in these
// cases. If there isn't, we can skip all these cases.
TypeInfo::HashCode mask =
type->full_hashcode & TypeInfo::CombinedHashCodeOf<SwitchCaseType<CASES>...>();
// HashCodeOf() ensures that two bits are always set for every hash, so we can quickly
// eliminate the bitmask where only one bit is set.
TypeInfo::HashCode two_bits = mask & (mask - 1);
if (two_bits) {
// There's a possibility. We need to scan further.
// Split the cases into two, and recurse.
constexpr size_t kMid = kNumCases / 2;
return NonDefaultCases(object, type, result, traits::Slice<0, kMid>(cases)) ||
NonDefaultCases(object, type, result,
traits::Slice<kMid, kNumCases - kMid>(cases));
} else {
return false;
}
}
}
/// The implementation of Switch() for all cases.
/// @see NonDefaultCases
template <typename T, typename RETURN_TYPE, typename... CASES>
inline void SwitchCases(T* object, RETURN_TYPE* result, std::tuple<CASES...>&& cases) {
using Cases = std::tuple<CASES...>;
static constexpr int kDefaultIndex = detail::IndexOfDefaultCase<Cases>();
static constexpr bool kHasDefaultCase = kDefaultIndex >= 0;
static constexpr bool kHasReturnType = !std::is_same_v<RETURN_TYPE, void>;
// Static assertions
static constexpr bool kDefaultIsOK =
kDefaultIndex == -1 || kDefaultIndex == static_cast<int>(std::tuple_size_v<Cases> - 1);
static constexpr bool kReturnIsOK =
kHasDefaultCase || !kHasReturnType || std::is_constructible_v<RETURN_TYPE>;
static_assert(kDefaultIsOK, "Default case must be last in Switch()");
static_assert(kReturnIsOK,
"Switch() requires either a Default case or a return type that is either void or "
"default-constructable");
// If the static asserts have fired, don't bother spewing more errors below
static constexpr bool kAllOK = kDefaultIsOK && kReturnIsOK;
if constexpr (kAllOK) {
if (object) {
auto* type = &object->TypeInfo();
if constexpr (kHasDefaultCase) {
// Evaluate non-default cases.
if (!detail::NonDefaultCases<T>(object, type, result,
traits::Slice<0, kDefaultIndex>(cases))) {
// Nothing matched. Evaluate default case.
if constexpr (kHasReturnType) {
new (result) RETURN_TYPE(
static_cast<RETURN_TYPE>(std::get<kDefaultIndex>(cases)({})));
} else {
std::get<kDefaultIndex>(cases)({});
}
}
} else {
if (!detail::NonDefaultCases<T>(object, type, result, std::move(cases))) {
// Nothing matched. No default case.
if constexpr (kHasReturnType) {
new (result) RETURN_TYPE();
}
}
}
} else {
// Object is nullptr, so no cases can match
if constexpr (kHasDefaultCase) {
// Evaluate default case.
if constexpr (kHasReturnType) {
new (result)
RETURN_TYPE(static_cast<RETURN_TYPE>(std::get<kDefaultIndex>(cases)({})));
} else {
std::get<kDefaultIndex>(cases)({});
}
} else {
// No default case, no case can match.
if constexpr (kHasReturnType) {
new (result) RETURN_TYPE();
}
}
}
}
}
/// Resolves to T if T is not nullptr_t, otherwise resolves to Ignore.
template <typename T>
using NullptrToIgnore = std::conditional_t<std::is_same_v<T, std::nullptr_t>, Ignore, T>;
/// Resolves to `const TYPE` if any of `CASE_RETURN_TYPES` are const or
/// pointer-to-const, otherwise resolves to TYPE.
template <typename TYPE, typename... CASE_RETURN_TYPES>
using PropagateReturnConst = std::conditional_t<
// Are any of the pointer-stripped types const?
(std::is_const_v<std::remove_pointer_t<CASE_RETURN_TYPES>> || ...),
const TYPE, // Yes: Apply const to TYPE
TYPE>; // No: Passthrough
/// SwitchReturnTypeImpl is the implementation of SwitchReturnType
template <bool IS_CASTABLE, typename REQUESTED_TYPE, typename... CASE_RETURN_TYPES>
struct SwitchReturnTypeImpl;
/// SwitchReturnTypeImpl specialization for non-castable case types and an
/// explicitly specified return type.
template <typename REQUESTED_TYPE, typename... CASE_RETURN_TYPES>
struct SwitchReturnTypeImpl</*IS_CASTABLE*/ false, REQUESTED_TYPE, CASE_RETURN_TYPES...> {
/// Resolves to `REQUESTED_TYPE`
using type = REQUESTED_TYPE;
};
/// SwitchReturnTypeImpl specialization for non-castable case types and an
/// inferred return type.
template <typename... CASE_RETURN_TYPES>
struct SwitchReturnTypeImpl</*IS_CASTABLE*/ false, Infer, CASE_RETURN_TYPES...> {
/// Resolves to the common type for all the cases return types.
using type = std::common_type_t<CASE_RETURN_TYPES...>;
};
/// SwitchReturnTypeImpl specialization for castable case types and an
/// explicitly specified return type.
template <typename REQUESTED_TYPE, typename... CASE_RETURN_TYPES>
struct SwitchReturnTypeImpl</*IS_CASTABLE*/ true, REQUESTED_TYPE, CASE_RETURN_TYPES...> {
public:
/// Resolves to `const REQUESTED_TYPE*` or `REQUESTED_TYPE*`
using type = PropagateReturnConst<std::remove_pointer_t<REQUESTED_TYPE>, CASE_RETURN_TYPES...>*;
};
/// SwitchReturnTypeImpl specialization for castable case types and an infered
/// return type.
template <typename... CASE_RETURN_TYPES>
struct SwitchReturnTypeImpl</*IS_CASTABLE*/ true, Infer, CASE_RETURN_TYPES...> {
private:
using InferredType =
CastableCommonBase<detail::NullptrToIgnore<std::remove_pointer_t<CASE_RETURN_TYPES>>...>;
public:
/// `const T*` or `T*`, where T is the common base type for all the castable
/// case types.
using type = PropagateReturnConst<InferredType, CASE_RETURN_TYPES...>*;
};
/// Resolves to the return type for a Switch() with the requested return type
/// `REQUESTED_TYPE` and case statement return types. If `REQUESTED_TYPE` is
/// Infer then the return type will be inferred from the case return types.
template <typename REQUESTED_TYPE, typename... CASE_RETURN_TYPES>
using SwitchReturnType = typename SwitchReturnTypeImpl<
IsCastable<NullptrToIgnore<std::remove_pointer_t<CASE_RETURN_TYPES>>...>,
REQUESTED_TYPE,
CASE_RETURN_TYPES...>::type;
} // namespace detail
/// Switch is used to dispatch one of the provided callback case handler
/// functions based on the type of `object` and the parameter type of the case
/// handlers. Switch will sequentially check the type of `object` against each
/// of the switch case handler functions, and will invoke the first case handler
/// function which has a parameter type that matches the object type. When a
/// case handler is matched, it will be called with the single argument of
/// `object` cast to the case handler's parameter type. Switch will invoke at
/// most one case handler. Each of the case functions must have the signature
/// `R(T*)` or `R(const T*)`, where `T` is the type matched by that case and `R`
/// is the return type, consistent across all case handlers.
///
/// An optional default case function with the signature `R(Default)` can be
/// used as the last case. This default case will be called if all previous
/// cases failed to match.
///
/// If `object` is nullptr and a default case is provided, then the default case
/// will be called. If `object` is nullptr and no default case is provided, then
/// no cases will be called.
///
/// Example:
/// ```
/// Switch(object,
/// [&](TypeA*) { /* ... */ },
/// [&](TypeB*) { /* ... */ });
///
/// Switch(object,
/// [&](TypeA*) { /* ... */ },
/// [&](TypeB*) { /* ... */ },
/// [&](Default) { /* Called if object is not TypeA or TypeB */ });
/// ```
///
/// @param object the object who's type is used to
/// @param cases the switch cases
/// @return the value returned by the called case. If no cases matched, then the
/// zero value for the consistent case type.
template <typename RETURN_TYPE = detail::Infer, typename T = CastableBase, typename... CASES>
inline auto Switch(T* object, CASES&&... cases) {
using ReturnType = detail::SwitchReturnType<RETURN_TYPE, traits::ReturnType<CASES>...>;
static constexpr bool kHasReturnType = !std::is_same_v<ReturnType, void>;
if constexpr (kHasReturnType) {
// Replacement for std::aligned_storage as this is broken on earlier versions of MSVC.
struct alignas(alignof(ReturnType)) ReturnStorage {
uint8_t data[sizeof(ReturnType)];
};
ReturnStorage storage;
auto* res = utils::Bitcast<ReturnType*>(&storage);
TINT_DEFER(res->~ReturnType());
detail::SwitchCases(object, res, std::forward_as_tuple(std::forward<CASES>(cases)...));
return *res;
} else {
detail::SwitchCases<T, void>(object, nullptr,
std::forward_as_tuple(std::forward<CASES>(cases)...));
}
}
} // namespace tint
TINT_CASTABLE_POP_DISABLE_WARNINGS();
#endif // SRC_TINT_CASTABLE_H_
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