[Rd] parent.frame(1) of a S4 method is not a calling environment.

[Vitaly S.]

Hadley Wickham <hadley at rice.edu> writes:

> On Tuesday, August 17, 2010, Vitaly S. <spinuvit.list at gmail.com> wrote:
>> Duncan Murdoch <murdoch.duncan at gmail.com> writes:
>>
>>> Vitaly S. wrote:
>>>> Martin Morgan <mtmorgan at fhcrc.org> writes:
>>>>
>>>>>> So,  can I be sure that for such functions parent.frame(2) will always work?
>>>>>> What are the additional rules?
>>>>>>
>>>>> callNextMethod() will cause additional problems; the idea that you'll
>>>>> grab things from somewhere other than function arguments doesn't seem
>>>>> like a robust design, even if it's used in some important parts of R.
>>>>>
>>>>> Martin
>>>>>
>>>>>
>>>>
>>>> That make it difficult to handle unevaluated expressions in methods. A solution
>>>> would be to explicitly require the users to use quote() or expression(),  and
>>>> then to use the "expression" in the signature. Slightly unpleasant, though.
>>>>
>>>>
>>>
>>> You could use formulas for that.  If you pass in
>>>
>>> formula = ~ x + y*z
>>>
>>> then environment(formula) will be the right evaluation environment, and formula[[2]] will be the unevaluated x +
>>> y*z.
>>>
>>> Duncan Murdoch
>>
>> Thank you Duncan, I didn't know that.
>>
>> For programmatic use though, formula interface is slightly inconvenient. A
>> specialized function and class would be desirable. With the advent of more and
>> more complex S4 classes, unevaluated expressions in methods calls will became a
>> necessity, that's my feeling.
>
> I probably should move the quoting related out of plyr into it's own
> package to facilitate this type of reuse. I think the current
> structure is quite general.

That would be neat. An S4 class "quote" which would store the parent.frame as a
slot would be great! 

>
> Hadley