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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_CASTABLE_H_
#define SRC_CASTABLE_H_
#include <utility>
#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();
namespace tint {
namespace detail {
template <typename T>
struct TypeInfoOf;
} // namespace detail
// Forward declaration
class CastableBase;
/// 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_CASTABLE_POP_DISABLE_WARNINGS()
/// 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;
/// @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.
bool Is(const tint::TypeInfo& type) const;
/// @returns the static TypeInfo for the type T
template <typename T>
static const TypeInfo& Of() {
return detail::TypeInfoOf<T>::info;
}
};
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;
};
// Forward declaration
template <typename TO_FIRST, typename... TO_REST>
struct IsAnyOf;
/// A placeholder structure used for template parameters that need a default
/// type, but can always be automatically inferred.
struct Infer;
} // namespace detail
/// 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,
};
/// @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) {
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");
if (obj == nullptr) {
return false;
}
if (upcast || nocast) {
return true;
}
return obj->TypeInfo().Is(TypeInfo::Of<std::remove_const_t<TO>>());
}
/// @returns true if `obj` is a valid pointer, and is of, or derives from the
/// class `TO`, and pred(const TO*) returns true
/// @param obj the object to test from
/// @param pred predicate function with signature `bool(const TO*)` called iff
/// object is of, or derives from the class `TO`.
/// @see CastFlags
template <typename TO,
int FLAGS = 0,
typename FROM = detail::Infer,
typename Pred = detail::Infer>
inline bool Is(FROM* obj, Pred&& pred) {
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;
static_assert(upcast || downcast || nocast, "impossible cast");
if (obj == nullptr) {
return false;
}
bool is_type = upcast || nocast ||
obj->TypeInfo().Is(TypeInfo::Of<std::remove_const_t<TO>>());
return is_type && pred(static_cast<std::add_const_t<TO>*>(obj));
}
/// @returns true if `obj` is of, or derives from any of the `TO`
/// classes.
/// @param obj the object to cast from
template <typename... TO, typename FROM>
inline bool IsAnyOf(FROM* obj) {
return detail::IsAnyOf<TO...>::Exec(obj);
}
/// @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&) = default;
/// Destructor
virtual ~CastableBase() = default;
/// 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 <typename TO, int FLAGS = 0, typename Pred = detail::Infer>
inline bool Is(Pred&& pred) const {
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 {
/// Helper for Castable::IsAnyOf
template <typename TO_FIRST, typename... TO_REST>
struct IsAnyOf {
/// @param obj castable object to test
/// @returns true if `obj` is of, or derives from any of `[TO_FIRST,
/// ...TO_REST]`
template <typename FROM>
static bool Exec(FROM* obj) {
return Is<TO_FIRST>(obj) || IsAnyOf<TO_REST...>::Exec(obj);
}
};
/// Terminal specialization
template <typename TO>
struct IsAnyOf<TO> {
/// @param obj castable object to test
/// @returns true if `obj` is of, or derives from TO
template <typename FROM>
static bool Exec(FROM* obj) {
return Is<TO>(obj);
}
};
} // namespace detail
} // namespace tint
TINT_CASTABLE_POP_DISABLE_WARNINGS();
#endif // SRC_CASTABLE_H_