ClickHouse/base/poco/Foundation/include/Poco/MetaObject.h

//
// MetaObject.h
//
// Library: Foundation
// Package: SharedLibrary
// Module:  ClassLoader
//
// Definition of the MetaObject class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_MetaObject_INCLUDED
#define Foundation_MetaObject_INCLUDED


#include <set>
#include "Poco/Exception.h"
#include "Poco/Foundation.h"
#include "Poco/SingletonHolder.h"


namespace Poco
{


template <class B>
class AbstractMetaObject
/// A MetaObject stores some information
/// about a C++ class. The MetaObject class
/// is used by the Manifest class.
/// AbstractMetaObject is a common base class
/// for all MetaObject in a rooted class hierarchy.
/// A MetaObject can also be used as an object
/// factory for its class.
{
public:
    AbstractMetaObject(const char * name) : _name(name) { }

    virtual ~AbstractMetaObject()
    {
        for (typename ObjectSet::iterator it = _deleteSet.begin(); it != _deleteSet.end(); ++it)
        {
            delete *it;
        }
    }

    const char * name() const { return _name; }

    virtual B * create() const = 0;
    /// Create a new instance of a class.
    /// Cannot be used for singletons.

    virtual B & instance() const = 0;
    /// Returns a reference to the only instance
    /// of the class. Used for singletons only.

    virtual bool canCreate() const = 0;
    /// Returns true iff the create method can be used
    /// to create instances of the class.
    /// Returns false if the class is a singleton.

    virtual void destroy(B * pObject) const
    /// If pObject was owned by meta object, the
    /// ownership of the deleted object is removed
    /// and the object is deleted.
    {
        typename ObjectSet::iterator it = _deleteSet.find(pObject);

        if (it != _deleteSet.end())
        {
            _deleteSet.erase(pObject);
            delete pObject;
        }
    }

    B * autoDelete(B * pObject) const
    /// Give ownership of pObject to the meta object.
    /// The meta object will delete all objects it owns
    /// when it is destroyed.
    ///
    /// Returns pObject.
    {
        if (this->canCreate()) // guard against singleton
        {
            poco_check_ptr(pObject);
            _deleteSet.insert(pObject);
        }
        else
            throw InvalidAccessException("Cannot take ownership of", this->name());

        return pObject;
    }

    virtual bool isAutoDelete(B * pObject) const
    /// Returns true if the object is owned
    /// by meta object.
    ///
    /// Overloaded in MetaSingleton - returns true
    /// if the class is a singleton.
    {
        return _deleteSet.find(pObject) != _deleteSet.end();
    }

private:
    AbstractMetaObject();
    AbstractMetaObject(const AbstractMetaObject &);
    AbstractMetaObject & operator=(const AbstractMetaObject &);

    typedef std::set<B *> ObjectSet;

    const char * _name;
    mutable ObjectSet _deleteSet;
};


template <class C, class B>
class MetaObject : public AbstractMetaObject<B>
/// A MetaObject stores some information
/// about a C++ class. The MetaObject class
/// is used by the Manifest class.
/// A MetaObject can also be used as an object
/// factory for its class.
{
public:
    MetaObject(const char * name) : AbstractMetaObject<B>(name) { }

    ~MetaObject() { }

    B * create() const { return new C; }

    B & instance() const { throw InvalidAccessException("Not a singleton. Use create() to create instances of", this->name()); }

    bool canCreate() const { return true; }
};


template <class C, class B>
class MetaSingleton : public AbstractMetaObject<B>
/// A SingletonMetaObject disables the create() method
/// and instead offers an instance() method to access
/// the single instance of its class.
{
public:
    MetaSingleton(const char * name) : AbstractMetaObject<B>(name) { }

    ~MetaSingleton() { }

    B * create() const
    {
        throw InvalidAccessException("Cannot create instances of a singleton class. Use instance() to obtain a", this->name());
    }

    bool canCreate() const { return false; }

    B & instance() const { return *_object.get(); }

    bool isAutoDelete(B * /*pObject*/) const { return true; }

private:
    mutable SingletonHolder<C> _object;
};


} // namespace Poco


#endif // Foundation_MetaObject_INCLUDED