foreach/opApply is the visitor pattern

[grauzone]

BCS wrote:
> Hello Robert,
> 
>> 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)
>>>
>> Er.... no. There's no double-dispatch (at least automatically),
>> there's only one foreach body delegate. The visitor pattern as far as
>> I know it uses dynamic dispatch so the visitor object can handle
>> different objects in the class hierarchy differently. For example, you
>> couldn't use a foreach to enumerate through a syntax tree and handle
>> expressions and statements differently (well, you could, but you'd
>> have to do it manually).
>>
> 
> OK I'll grant that it doesn't follow the normal pattern to the letter 
> but it can be viewed as a degenerate case where there is only one 
> visitable type.

Does that mean all function calls are a degenerate case of the visitor 
pattern?