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#pragma once
#include <cassert>
#include <functional>
#include <memory>
#include <type_traits>
namespace cru {
template <typename T>
class SelfResolvable;
template <typename T>
class ObjectResolver {
friend SelfResolvable<T>;
template <typename U>
friend class ObjectResolver;
private:
template <typename U>
using Accessor_ = std::function<U*(const std::shared_ptr<void*>&)>;
using ThisAccessor_ = Accessor_<T>;
explicit ObjectResolver(T* o)
: shared_object_ptr_(new void*(o)),
accessor_([](const std::shared_ptr<void*>& ptr) {
return static_cast<T*>(*ptr);
}) {}
explicit ObjectResolver(std::shared_ptr<void*> ptr, ThisAccessor_ accessor)
: shared_object_ptr_(std::move(ptr)), accessor_(std::move(accessor)) {}
template <typename U>
static ThisAccessor_ CreateAccessor(Accessor_<U> parent_accessor) {
return [parent_accessor =
std::move(parent_accessor)](const std::shared_ptr<void*>& ptr) {
return static_cast<T*>(parent_accessor(ptr));
};
}
public:
template <typename U,
typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
ObjectResolver(const ObjectResolver<U>& other)
: shared_object_ptr_(other.shared_object_ptr_),
accessor_(CreateAccessor(other.accessor_)) {}
template <typename U,
typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
ObjectResolver(ObjectResolver<U>&& other)
: shared_object_ptr_(std::move(other.shared_object_ptr_)),
accessor_(CreateAccessor(std::move(other.accessor_))) {}
ObjectResolver(const ObjectResolver&) = default;
ObjectResolver& operator=(const ObjectResolver&) = default;
ObjectResolver(ObjectResolver&&) = default;
ObjectResolver& operator=(ObjectResolver&&) = default;
~ObjectResolver() = default;
template <typename U,
typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
ObjectResolver& operator=(const ObjectResolver<U>& other) {
if (this != &other) {
this->shared_object_ptr_ = other.shared_object_ptr_;
this->accessor_ = CreateAccessor(other.accessor_);
}
return *this;
}
template <typename U,
typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
ObjectResolver& operator=(ObjectResolver<U>&& other) {
if (this != &other) {
this->shared_object_ptr_ = std::move(other.shared_object_ptr_);
this->accessor_ = CreateAccessor(std::move(other.shared_object_ptr_));
}
return *this;
}
bool IsValid() const { return this->shared_object_ptr_ != nullptr; }
T* Resolve() const {
assert(IsValid());
return this->accessor_(this->shared_object_ptr_);
}
/**
* @remarks So this class can be used as a functor.
*/
T* operator()() const { return Resolve(); }
template <typename U,
typename = std::enable_if_t<std::is_convertible_v<T*, U*>>>
operator ObjectResolver<U>() const {
return ObjectResolver<U>(*this);
}
private:
void SetResolvedObject(T* o) {
assert(IsValid());
*this->shared_object_ptr_ = o;
}
private:
std::shared_ptr<void*> shared_object_ptr_;
std::function<T*(const std::shared_ptr<void*>&)> accessor_;
};
/**
* @remarks
* This class is not copyable and movable since subclass is polymorphic and
* copying is then nonsense. However, you can even delete move capability in
* subclass because it may also be nonsense for subclass. The move capability is
* optional.
*
* Whether this class needs to be thread-safe still has to be considered.
*/
template <typename T>
class SelfResolvable {
public:
SelfResolvable() : resolver_(CastToSubClass()) {}
SelfResolvable(const SelfResolvable&) = delete;
SelfResolvable& operator=(const SelfResolvable&) = delete;
// Resolvers to old object will resolve to new object.
SelfResolvable(SelfResolvable&& other)
: resolver_(std::move(other.resolver_)) {
this->resolver_.SetResolvedObject(CastToSubClass());
}
// Old resolvers for this object will resolve to nullptr.
// Other's resolvers will now resolve to this.
SelfResolvable& operator=(SelfResolvable&& other) {
if (this != &other) {
this->resolver_ = std::move(other.resolver_);
this->resolver_.SetResolvedObject(CastToSubClass());
}
return *this;
}
virtual ~SelfResolvable() {
if (this->resolver_.IsValid()) {
this->resolver_.SetResolvedObject(nullptr);
}
}
ObjectResolver<T> CreateResolver() { return resolver_; }
private:
T* CastToSubClass() { return static_cast<T*>(this); }
private:
ObjectResolver<T> resolver_;
};
} // namespace cru
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