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// Copyright 2020 The Dawn & Tint Authors
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef SRC_DAWN_COMMON_REFBASE_H_
#define SRC_DAWN_COMMON_REFBASE_H_
#include <type_traits>
#include <utility>
#include "dawn/common/Assert.h"
#include "dawn/common/Compiler.h"
namespace dawn {
// A common class for various smart-pointers acting on referenceable/releasable pointer-like
// objects. Logic for each specialization can be customized using a Traits type that looks
// like the following:
//
// struct {
// static constexpr T kNullValue = ...;
// static void Reference(T value) { ... }
// static void Release(T value) { ... }
// };
//
// RefBase supports
template <typename T, typename Traits>
class RefBase {
public:
// Default constructor and destructor.
RefBase() : mValue(Traits::kNullValue) {}
~RefBase() { Release(mValue); }
// Constructors from nullptr.
// NOLINTNEXTLINE(runtime/explicit)
constexpr RefBase(std::nullptr_t) : RefBase() {}
RefBase<T, Traits>& operator=(std::nullptr_t) {
Set(Traits::kNullValue);
return *this;
}
// Constructors from a value T.
// NOLINTNEXTLINE(runtime/explicit)
RefBase(T value) : mValue(value) { Reference(value); }
RefBase<T, Traits>& operator=(const T& value) {
Set(value);
return *this;
}
// Constructors from a RefBase<T>
RefBase(const RefBase<T, Traits>& other) : mValue(other.mValue) { Reference(other.mValue); }
RefBase<T, Traits>& operator=(const RefBase<T, Traits>& other) {
Set(other.mValue);
return *this;
}
RefBase(RefBase<T, Traits>&& other) { mValue = other.Detach(); }
RefBase<T, Traits>& operator=(RefBase<T, Traits>&& other) {
if (&other != this) {
Release(mValue);
mValue = other.Detach();
}
return *this;
}
// Constructors from a RefBase<U>. Note that in the *-assignment operators this cannot be the
// same as `other` because overload resolution rules would have chosen the *-assignement
// operators defined with `other` == RefBase<T, Traits>.
template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
RefBase(const RefBase<U, UTraits>& other) : mValue(other.mValue) {
Reference(other.mValue);
}
template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
RefBase<T, Traits>& operator=(const RefBase<U, UTraits>& other) {
Set(other.mValue);
return *this;
}
template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
RefBase(RefBase<U, UTraits>&& other) {
mValue = other.Detach();
}
template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
RefBase<T, Traits>& operator=(RefBase<U, UTraits>&& other) {
Release(mValue);
mValue = other.Detach();
return *this;
}
// Comparison operators.
bool operator==(const T& other) const { return mValue == other; }
bool operator!=(const T& other) const { return mValue != other; }
const T operator->() const { return mValue; }
T operator->() { return mValue; }
bool operator<(const RefBase<T, Traits>& other) const { return mValue < other.mValue; }
// Smart pointer methods.
const T& Get() const { return mValue; }
T& Get() { return mValue; }
[[nodiscard]] T Detach() {
T value{std::move(mValue)};
mValue = Traits::kNullValue;
return value;
}
void Acquire(T value) {
Release(mValue);
mValue = value;
}
[[nodiscard]] T* InitializeInto() {
DAWN_ASSERT(mValue == Traits::kNullValue);
return &mValue;
}
private:
// Friend is needed so that instances of RefBase<U> can call Reference and Release on
// RefBase<T>.
template <typename U, typename UTraits>
friend class RefBase;
static void Reference(T value) {
if (value != Traits::kNullValue) {
Traits::Reference(value);
}
}
static void Release(T value) {
if (value != Traits::kNullValue) {
Traits::Release(value);
}
}
void Set(T value) {
if (mValue != value) {
// Ensure that the new value is referenced before the old is released to prevent any
// transitive frees that may affect the new value.
Reference(value);
Release(mValue);
mValue = value;
}
}
T mValue;
};
} // namespace dawn
#endif // SRC_DAWN_COMMON_REFBASE_H_