On Monday, 27 August 2012 at 16:28:24 UTC, deadalnix wrote:
Le 27/08/2012 18:02, Michal Minich a écrit :
On Monday, 27 August 2012 at 15:00:11 UTC, deadalnix wrote:
/!\ Shameless autopromotion incoming /!\
I have recently put some effort into exploring alternatives
to visitor
pattern and see what can be done in D. I ended up with a
solution
which is a real improvement compared to plein old visitor
pattern and
wanted to share this here.
I think this is short enough to be a good example to show
what can be
done with D capabilities.
http://www.deadalnix.me/2012/08/25/visitor-pattern-revisited-in-d/
This is nice use of d magic. If the implementation could
recompute the
functions pointers during compilation, this seems as nice
generally
function. This makes me thing of computed goto (to functions)
One possibility to achieve this result for visitor is to use
mixin.
I would mixin implementation of accept method into very node
super
class. This is to avoid code duplication.
Secondly, I would mixin implementation of opDispatch that
simply does
nothing/throws to every implementation of visitor. This is to
avoid
empty implementations of visit methods which are not needed for
particular visitor.
This can only work if you know all node type by advance. Which
is one limitation of the visitor pattern I intended to solve.
The opDispatch would only handle non existing methods in visitor.
It could be defined to throw, or each visitor could define one
doing generic thing for that visitor (ie return null), or visitor
could not use opDispatch at all.
Generally I think default imlementations of interface methods -
such as to throw/do nothing/return null should not be used. Then
I think is better to split the interface/hierarchy of clases.
This may not be allways better solution. Large hierarchy of
clases can be hiding some middle clases, wich could lead to
beterr desing, if lucky. But here it depend on specifics if its
better to introduce hierarchy, or handle some specifics here and
there.
