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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