Re: [wxhaskell-devel] virtual methods

[Kristof B. <kr...@re...>]

That would need the FlexibleInstances extension though.

On 14-05-15 14:11, Kristof Bastiaensen wrote:
> Hi,
>
> Looking at the source code, it seems that virtual member functions are 
> not supported yet by wxHaskell.
> I've been thinking about several solutions, and I have come up with a 
> solution that seems reasonable:
>
> For example to subclass wxGridCellRenderer, define a typeclass 
> gridCellRenderer and a newGridCellRenderer contructor:
>
> class WxGridCellRenderer where
>    wxGridCellRendererDraw :: wxGrid a -> wxGridCellAttr 
> <http://docs.wxwidgets.org/3.0/classwx_grid_cell_attr.html> -> wxDC 
> <http://docs.wxwidgets.org/3.0/classwx_d_c.html> Rect 
> <http://docs.wxwidgets.org/3.0/classwx_rect.html> -> Int -> Int -> 
> Bool -> IO ()
>    wxGridCellRendererDraw = wxGridCellRenderDrawDefault
>    wxGridCellRendererGetBestSize :: (..)
>    wxGridCellRendererGetBestSize = wxGridCellRendererGetBestSizeDefault
>    (...)
>
> newGridCellRenderer :: (WxGridCellRenderer a) => IO a
>
> This creates a new gridCellRenderer, were the virtual functions call 
> the functions in the instance.
>
> On the C side, create a subclass, with a constructor that takes the 
> function definitions for all the virtual functions.  The default 
> definitions are simply the base class functions 
> WxGridCellRenderer::Draw(), etc...
>
> It does need a lot of boilerplate, that may be automated via wxdirect.
>
> -- Kristof Bastiaensen
>
>
>
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