attribute bag class

[3doutpost]

looking for some advice on design here - i can do what i want using
casts but it feels wrong and it seems like there must be a better way.

i have some 'things' that need to be rendered to the display but the
way that happens will probably vary over time and each 'thing'
requires a different parameter - say colour for instance.

so, i have a renderer class derrived from an abstract renderer class
with a single pure virtual method called render ()

i also have a rendererAttr class derrived from a base rendererAttr
class with no pure virtual methods since there isn't anything that
will obviously be shared - e.g. this default might use colors but
another implementation might use bitmaps or something.

when creating and processing the 'things', i pass around pointers to
my base renderer and rendererAttr but eventually i need to downcast to
my rendererAttr implementation so i can call non-virtual methods on
it..

i don't know if this is clear without code - i guess what i'm wanting
is pattern that descibes how you create an "action" class and an
"attribute" class and make the two work together without the nasty
downcasting..

any comments?