foreach/opApply is the visitor pattern

[Spacen Jasset]

grauzone wrote:
> BCS wrote:
>> Correct me if I'm wrong but I thing that D's opApply is a form of the 
>> Visitor pattern where the calling function's stack frame is the 
>> visitor object.
>>
>> This just occurred to me. Maybe I've been missing something re the 
>> visitor pattern but I think this make for a nice, cool and easy way to 
>> describe it. (Also I don't remember it being described that way)
> 
> More importantly, why does it matter?
Because there is a difference? opApply is more like a functor. Not the 
visitor pattern in my view of things.

They are/can be used to solve different things.

The visitor pattern commonly can be used to avoid case object.type: 
situations, to deal with different object types. Whereas a functor is 
used for other things, like iteration.