Re: [boost] interest in properties library

Subject: Re: [boost] interest in properties library
From: Daniel Oberhoff (daniel.oberhoff_at_[hidden])
Date: 2008-12-20 08:29:53

> On Fri, Dec 19, 2008 at 5:50 AM, Daniel Oberhoff <
> daniel.oberhoff_at_[hidden]> wrote:
> > Hi,
> >
> > I am thinking about submitting a library proposal and would like  
> to query
> > wether there is any interest in such a library and chance of  
> success of such
> > a proposal.
> >
> > The basic idea is to implement the possibility to decorate a class  
> with
> > named properties, such that given a pointer to an instance  
> properties can be
> > accessed by name rather than using set/get methods. Also the type  
> of the
> > instance should not need to be known at compile time, other than  
> that it
> > derives from a suitable base class describing the property  
> mechanisms.
> >
> > There is a rough implementation existing and used in a product  
> environment.
> > Setting and getting is done using appropriate boost functions. Type
> > resolution is done using RTTI (especially dynamic cast). Complex  
> inheritance
> > hierarchies are supported through virtual inheritance from the  
> base class,
> > such that several classes along the hierarchy can contribute  
> property slots.
> > CRTP and static initialization is used to register properties.  
> Convenient
> > setter/getter function generators are provided as is a mechanism  
> to access
> > nested properties using dot notation.
>
> I'm not sure I follow exactly what you mean, could you give a small  
> example
> of the interface and usage? It sounds like you are referring to  
> something
> along the lines of C# properties though I don't immediately see what  
> you are
> using dynamic casting for or what exactly this provides as a benefit  
> over
> get/set methods. Thanks.

sorry, forgot the examples. so, to enable properties for a class:

class Foo : public HasProperties<VariantTypes, foo>
{

protected:

        typedef HasProperties<VariantTypes, foo> PBase;
        typedef Foo This;

        static void init_properties()
        {
                PBase::add_ivar_property_rw( "a", &This::a );
        }

private:

                int a;

};

usage:

HasPropertiesBase<VariantTypes> * foo = new Foo;
foo->set_property("a", 1);
int a = get<int>( foo->get_property( "a" ) );

Here VariantTyped is a mpl::sequence

Furthermore it still works when a class has several such properties  
activated classes along its inheritance ancestors, and all properties  
can be acessed unless there is a name conflict, in which case classes  
further down override properties from its ancestors, though this could  
be handled differently.

What I still want to do is enable simpler syntax and maybe signals  
triggered by property and other goodies, but that is actually rather  
simple to do, using bind and/or lambda.

Best

Daniel