Re: Creating properties in Lua-only classes

I'll rephrase my question, with code this time:

I have a C++ class, bound to Lua along these lines:

luabind::class_<Window>( "Window" )

.def( luabind::constructor<>( ) )

.property( "height", &Window::GetHeight, &Window::SetHeight )

.property( "width", &Window::GetWidth, &Window::SetWidth );

/** wrap_base forwarding class omitted **/


Of course, in Lua this means I can do the following:

win = Window()
win.width = 320        -- calls setter
print( win.width )       -- calls getter

Now, I would like to allow a client to subclass Window from within Lua,
overriding the setters and/or getters with Lua functions, something like
this:

class 'SubWindow' (Window)

function SubWindow:SetHeight( newHeight )

Window.SetHeight( self, newHeight )
--  other stuff

end

function SubWindow:SetWidth( newWidth )

Window.SetWidth( self, newWidth )
--  other stuff

end


function SubWindow:__init( )

Window.__init(self)
--[[
    magically bind derived SetHeight( ) and SetWidth( ) to __newindex
metamethod
--]]

end

win = SubWindow()
win.width = 320        -- calls SubWindow's setter
print( win.width )       -- calls Window's getter


As you can see, the only way I can think to do this would be by overriding
the __index and __newindex metamethods on the derived class, but because
Luabind classes are userdata, this seems impossible at the moment.  I know
the last comment I read from this list on the subject said it might possibly
be implemented with version .9 (even though firm plans were only for 1.0) -
has that happened?

If not, is there a distinct mechanism within Luabind to override properties
in derived classes?  I remember seeing a comment in the source saying that
properties should "always be overridden, not overloaded", but I couldn't
discern how the overriding would happen in the first place.

Thanks,
-Nick



On Tue, Feb 8, 2011 at 12:06 PM, Kitten, Nicholas
<[email protected]>wrote:

> Does anyone know how I would go about creating a property within a
> Lua-created class (using Lua functions for getters and setters)?  I'm
> guessing there's support in the metatables for doing it, but I've never seen
> an implementation.
>
> Thanks,
> -Nick
>

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