cocos_lib/cocos/base/Ptr.h

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// Originally the class is from WebRTC.
// https://chromium.googlesource.com/external/webrtc/+/master/api/scoped_refptr.h
//

// A smart pointer class for reference counted objects.  Use this class instead
// of calling addRef and Release manually on a reference counted object to
// avoid common memory leaks caused by forgetting to Release an object
// reference.  Sample usage:
//
//   class MyFoo : public RefCounted<MyFoo> {
//    ...
//   };
//
//   void some_function() {
//     IntrusivePtr<MyFoo> foo = ccnew MyFoo();
//     foo->Method(param);
//     // `foo` is released when this function returns
//   }
//
//   void some_other_function() {
//     IntrusivePtr<MyFoo> foo = ccnew MyFoo();
//     ...
//     foo = nullptr;  // explicitly releases `foo`
//     ...
//     if (foo)
//       foo->Method(param);
//   }
//
// The above examples show how IntrusivePtr<T> acts like a pointer to T.
// Given two IntrusivePtr<T> classes, it is also possible to exchange
// references between the two objects, like so:
//
//   {
//     IntrusivePtr<MyFoo> a = ccnew MyFoo();
//     IntrusivePtr<MyFoo> b;
//
//     b.swap(a);
//     // now, `b` references the MyFoo object, and `a` references null.
//   }
//
// To make both `a` and `b` in the above example reference the same MyFoo
// object, simply use the assignment operator:
//
//   {
//     IntrusivePtr<MyFoo> a = ccnew MyFoo();
//     IntrusivePtr<MyFoo> b;
//
//     b = a;
//     // now, `a` and `b` each own a reference to the same MyFoo object.
//   }
//

#pragma once

#include <utility>
#include "cocos/base/std/hash/hash_fwd.hpp"

namespace cc {

template <class T>
class IntrusivePtr {
public:
    using element_type = T;

    IntrusivePtr() {
    }

    IntrusivePtr(T *p) : _ptr(p) { // NOLINT
        if (_ptr) {
            _ptr->addRef();
        }
    }

    IntrusivePtr(const IntrusivePtr<T> &r) : _ptr(r._ptr) {
        if (_ptr) {
            _ptr->addRef();
        }
    }

    template <typename U>
    IntrusivePtr(const IntrusivePtr<U> &r) : _ptr(r.get()) { // NOLINT
        if (_ptr) {
            _ptr->addRef();
        }
    }

    // Move constructors.
    IntrusivePtr(IntrusivePtr<T> &&r) noexcept : _ptr(r.release()) {
    }

    template <typename U>
    IntrusivePtr(IntrusivePtr<U> &&r) noexcept : _ptr(r.release()) { // NOLINT
    }

    ~IntrusivePtr() {
        if (_ptr) {
            _ptr->release();
        }
    }

    T *get() const { return _ptr; }
    operator T *() const { return _ptr; } // NOLINT
    T &operator*() const { return *_ptr; }
    T *operator->() const { return _ptr; }

    // As reference count is 1 after creating a RefCounted object, so do not have to
    // invoke p->addRef();
    IntrusivePtr<T> &operator=(T *p) {
        reset(p);
        return *this;
    }

    IntrusivePtr<T> &operator=(const IntrusivePtr<T> &r) { // NOLINT
        return *this = r._ptr;                             // NOLINT
    }

    template <typename U>
    IntrusivePtr<T> &operator=(const IntrusivePtr<U> &r) {
        return *this = r.get(); // NOLINT
    }

    IntrusivePtr<T> &operator=(IntrusivePtr<T> &&r) noexcept {
        IntrusivePtr<T>(std::move(r)).swap(*this);
        return *this;
    }

    template <typename U>
    IntrusivePtr<T> &operator=(IntrusivePtr<U> &&r) noexcept {
        IntrusivePtr<T>(std::move(r)).swap(*this);
        return *this;
    }

    bool operator==(std::nullptr_t) {
        return _ptr == nullptr;
    }

    bool operator==(T *r) {
        return _ptr == r;
    }

    bool operator!=(std::nullptr_t) {
        return _ptr != nullptr;
    }

    bool operator!=(T *r) {
        return _ptr != r;
    }

    void reset() noexcept {
        if (_ptr) {
            _ptr->release();
        }
        _ptr = nullptr;
    }

    void reset(T *p) {
        // AddRef first so that self assignment should work
        if (p) {
            p->addRef();
        }
        if (_ptr) {
            _ptr->release();
        }
        _ptr = p;
    }

    void swap(T **pp) noexcept {
        T *p = _ptr;
        _ptr = *pp;
        *pp = p;
    }

    void swap(IntrusivePtr<T> &r) noexcept { swap(&r._ptr); }

private:
    // Returns the (possibly null) raw pointer, and makes the scoped_refptr hold a
    // null pointer, all without touching the reference count of the underlying
    // pointed-to object. The object is still reference counted, and the caller of
    // release() is now the proud owner of one reference, so it is responsible for
    // calling Release() once on the object when no longer using it.
    T *release() {
        T *retVal = _ptr;
        _ptr = nullptr;
        return retVal;
    }

protected:
    T *_ptr{nullptr};
};

} // namespace cc

namespace ccstd {

template <class T>
struct hash<cc::IntrusivePtr<T>> {
    hash_t operator()(const cc::IntrusivePtr<T> &val) const noexcept {
        return hash<T *>{}(val.get());
    }
};

} // namespace ccstd