juce_WeakReference.h

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 /*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited
 
   JUCE is an open source library subject to commercial or open-source
   licensing.
 
   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.
 
   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.
 
  ==============================================================================
*/
 
namespace juce
{
 
//==============================================================================
template <class ObjectType, class ReferenceCountingType = ReferenceCountedObject>
class WeakReference
{
public:
    inline WeakReference() = default;
 
    WeakReference (ObjectType* object)  : holder (getRef (object)) {}
 
    WeakReference (const WeakReference& other) noexcept         : holder (other.holder) {}
 
    WeakReference (WeakReference&& other) noexcept              : holder (std::move (other.holder)) {}
 
    WeakReference& operator= (const WeakReference& other)       { holder = other.holder; return *this; }
 
    WeakReference& operator= (ObjectType* newObject)            { holder = getRef (newObject); return *this; }
 
    WeakReference& operator= (WeakReference&& other) noexcept   { holder = std::move (other.holder); return *this; }
 
    ObjectType* get() const noexcept                            { return holder != nullptr ? holder->get() : nullptr; }
 
    operator ObjectType*() const noexcept                       { return get(); }
 
    ObjectType* operator->() const noexcept                     { return get(); }
 
    bool wasObjectDeleted() const noexcept                      { return holder != nullptr && holder->get() == nullptr; }
 
    //==============================================================================
    class SharedPointer   : public ReferenceCountingType
    {
    public:
        explicit SharedPointer (ObjectType* obj) noexcept : owner (obj) {}
 
        inline ObjectType* get() const noexcept     { return owner; }
        void clearPointer() noexcept                { owner = nullptr; }
 
    private:
        ObjectType* owner;
 
        JUCE_DECLARE_NON_COPYABLE (SharedPointer)
    };
 
    using SharedRef = ReferenceCountedObjectPtr<SharedPointer>;
 
    //==============================================================================
    class Master
    {
    public:
        Master() = default;
 
        ~Master() noexcept
        {
            // You must remember to call clear() in your source object's destructor! See the notes
            // for the WeakReference class for an example of how to do this.
            jassert (sharedPointer == nullptr || sharedPointer->get() == nullptr);
        }
 
        SharedRef getSharedPointer (ObjectType* object)
        {
            if (sharedPointer == nullptr)
            {
                sharedPointer = *new SharedPointer (object);
            }
            else
            {
                // You're trying to create a weak reference to an object that has already been deleted!!
                jassert (sharedPointer->get() != nullptr);
            }
 
            return sharedPointer;
        }
 
        void clear() noexcept
        {
            if (sharedPointer != nullptr)
                sharedPointer->clearPointer();
        }
 
        int getNumActiveWeakReferences() const noexcept
        {
            return sharedPointer == nullptr ? 0 : (sharedPointer->getReferenceCount() - 1);
        }
 
    private:
        SharedRef sharedPointer;
 
        JUCE_DECLARE_NON_COPYABLE (Master)
    };
 
private:
    SharedRef holder;
 
    static SharedRef getRef (ObjectType* o)
    {
        if (o != nullptr)
            return o->masterReference.getSharedPointer (o);
 
        return {};
    }
};
 
 
//==============================================================================
#define JUCE_DECLARE_WEAK_REFERENCEABLE(Class) \
    struct WeakRefMaster  : public juce::WeakReference<Class>::Master { ~WeakRefMaster() { this->clear(); } }; \
    WeakRefMaster masterReference; \
    friend class juce::WeakReference<Class>; \
 
 
} // namespace juce