cow.h

/*
 * Copyright (C) 2018 Microchip Technology Inc.  All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#ifndef EGT_DETAIL_COW_H
#define EGT_DETAIL_COW_H
 
#include <egt/detail/meta.h>
#include <memory>
 
namespace egt
{
inline namespace v1
{
namespace detail
{
 
template <class T>
class CopyOnWriteAllocate
{
public:
 
    CopyOnWriteAllocate() = default;
 
    explicit CopyOnWriteAllocate(T* t)
        : m_ptr(t)
    {}
 
    explicit CopyOnWriteAllocate(const std::shared_ptr<T>& refptr)
        : m_ptr(refptr)
    {}
 
    explicit operator bool() const
    {
        return !!m_ptr;
    }
 
    const T& operator*() const
    {
        allocate();
        return *m_ptr;
    }
 
    T& operator*()
    {
        detach();
        return *m_ptr;
    }
 
    const T* operator->() const
    {
        allocate();
        return m_ptr.operator->();
    }
 
    T* operator->()
    {
        detach();
        return m_ptr.operator->();
    }
 
private:
 
    void allocate()
    {
        if (!m_ptr)
            m_ptr = std::make_shared<T>();
    }
 
    void detach()
    {
        if (!m_ptr)
            allocate();
        else if (m_ptr && !m_ptr.unique())
            m_ptr = std::make_shared<T>(*m_ptr);
    }
 
    std::shared_ptr<T> m_ptr;
};
 
}
}
}
 
#endif