[geos-devel] Question about geos::io::Unload::Release()

[strk at refractions.net]

On Sun, Mar 12, 2006 at 12:45:31PM +0100, Mateusz Å?oskot wrote:
> strk at refractions.net wrote:
> >static lifetime should be ok. I dunno if it's used by client code,
> >anyway it might be useful to have a 'default' factory to use instead 
> >of having to construct (and maintain alive) a custom one. I'd move
> >access to it to GeometryFactory::defaultInstance()
> 
> I see the idea behind default factory.
> So, I'd make it a singleton, constructed on first request of its 
> instance. As I understand defaultInstance() is sucha a solution.
> The only problem is to properly define Singleton class.
> 
> Here is some simple proposal:

... mmm .. simple ? :)
How about:

class PrecisionModel { 
public:
	.....
	const PrecisionModel* defaultInstance() {
		static PrecisionModel defInstance(PrecisionModel::defaultInstance());
		return &defInstance;
	}
};

class GeometryFactory { 
public:
	.....
	const GeometryFactory* defaultInstance() {
		static GeometryFactory defInstance(PrecisionModel::defaultInstance());
		return &defInstance;
	}
};

--strk;


> 
> template<class T>
> class Singleton
> {
> private:
> 
>     class InstancePtr
>     {
>     public:
>         InstancePtr() : m_ptr(0) {}
>         ~InstancePtr() { delete m_ptr; }
> 
>         T* Get()
>         {
>             return m_ptr;
>         }
> 
>         void Set(T* p)
>         {
>             if(p!= 0)
>             {
>                 if (m_ptr != 0)
>                 {
>                     delete m_ptr;
>                 }
>                 m_ptr = p;
>             }
>         }
> 
>     private:
> 
>         T* m_ptr;
>     };
> 
>     static InstancePtr m_instptr;
> 
>     Singleton();
> 
>     Singleton(const Singleton&);
> 
>     Singleton& operator=(const Singleton&);
> 
> public:
> 
>     static T* Instance()
>     {
>         if(m_instptr.Get() == 0)
>         {
>             m_instptr.Set(new T());
>         }
>         return m_instptr.Get();
>     }
> };
> 
> But it may be better defined using smart pointers as well.
> 
> Cheers
> -- 
> Mateusz Łoskot
> http://mateusz.loskot.net
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> geos-devel mailing list
> geos-devel at geos.refractions.net
> http://geos.refractions.net/mailman/listinfo/geos-devel

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