LazyPointer.h

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/*
 * This file is a part of the Biology project by eons LLC.
 * Biology (aka Develop Biology) is a framework for approaching software
 * development from a natural sciences perspective.
 *
 * Copyright (C) 2026 Séon O'Shannon & eons LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include <cstddef>
 
namespace bio {
 
template < typename T >
class LazyPointer
{
public:
    typedef T* (*Factory)();
 
    LazyPointer()
        :
        mPtr(NULL),
        mFactory(NULL)
    {
    }
 
    explicit LazyPointer(Factory factory)
        :
        mPtr(NULL),
        mFactory(factory)
    {
    }
 
    explicit LazyPointer(T* materialized)
        :
        mPtr(materialized),
        mFactory(NULL)
    {
    }
 
    LazyPointer(const LazyPointer& other)
        :
        mPtr(NULL),
        mFactory(other.mFactory)
    {
        // Clone gets a fresh empty cache + the source's factory; first
        // access re-materialises. Matches Wave copy-ctor semantics.
    }
 
    LazyPointer& operator=(const LazyPointer& other)
    {
        if (this != &other)
        {
            if (mPtr)
            {
                delete mPtr;
                mPtr = NULL;
            }
            mFactory = other.mFactory;
        }
        return *this;
    }
 
    ~LazyPointer()
    {
        if (mPtr)
        {
            delete mPtr;
        }
    }
 
    T* operator->() const
    {
        if (!mPtr && mFactory)
        {
            mPtr = mFactory();
        }
        return mPtr;
    }
 
    T& operator*() const
    {
        return *operator->();
    }
 
    T* Get() const
    {
        return operator->();
    }
 
    T* GetIfMaterialized() const
    {
        return mPtr;
    }
 
    bool IsMaterialized() const
    {
        return mPtr != NULL;
    }
 
    void SetFactory(Factory factory)
    {
        mFactory = factory;
    }
 
    Factory GetFactory() const
    {
        return mFactory;
    }
 
    void ResetWith(T* materialized)
    {
        if (mPtr == materialized)
        {
            return;
        }
        if (mPtr)
        {
            delete mPtr;
        }
        mPtr = materialized;
    }
 
    T* Release()
    {
        T* p = mPtr;
        mPtr = NULL;
        return p;
    }
 
private:
    mutable T* mPtr;
    Factory mFactory;
};
 
} // namespace bio