Visitor pattern revisited in D

[Timon Gehr]

On 08/29/2012 02:24 AM, deadalnix wrote:
> Le 28/08/2012 17:39, Timon Gehr a écrit :
>> On 08/27/2012 05:00 PM, 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/
>>
>> An issue is that the proposed scheme does not support subclassing a
>> node to tweak its behaviour without changing the way the visitor
>> operates on it. i.e. it violates the substitution principle by default.
>>
>
> It does indeed. This is why I started by stating that we are interested
> in object as data abstraction here, not as behavioral one.
> ...

There is no obvious difference between data and behaviour.

class A: Node{
     auto visit(...){...}
     int getFoo(){ return foo; }
}

class B: A{
     override int getFoo(){ return 2*foo; }
}