[wxhaskell-devel] virtual methods

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

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