[Rd] question about assignment warnings for replacement methods

[Hervé Pagès]

Hi Simon,

On 11-04-08 01:05 PM, Simon Urbanek wrote:
>
> On Apr 8, 2011, at 2:55 PM, Hervé Pagès wrote:
>
>> Hi Duncan, Marc,
>>
>> On 11-04-05 11:15 AM, Duncan Murdoch wrote:
>>> On 05/04/2011 1:51 PM, Marc Carlson wrote:
>>>> Hi,
>>>>
>>>> I have seen several packages that with the most recent version of R are
>>>> giving a warning like this:
>>>>
>>>> Assignments in \usage in documentation object 'marginalData-methods':
>>>> marginalData(object) = value
>>>>
>>>> I assume that this is to prevent people from making assignments in their
>>>> usage statements (which seems completely understandable). But what
>>>> about the case above? This is a person who just wants to show the
>>>> proper usage for a replacement method. IOW they just want to write
>>>> something that looks like what you actually do when you use a
>>>> replacement method. They just want to show users how to do something
>>>> like this:
>>>>
>>>> replacementMethod(object)<- newValue
>>>>
>>>>
>>>> So is that really something that should not be allowed in a usage
>>>> statement?
>>>
>>> If replacementMethod was a replacement function, then
>>>
>>> replacementMethod(object)<- newValue
>>>
>>> is supposed to be fine.
>>
>> Yes, 'replacementMethod(object)<- newValue' vorks indeed, but
>> not 'replacementMethod(object) = newValue'.
>>
>>> But if it is an S3 method, it should be
>>>
>>> \method{replacementMethod}{class}(object)<- newValue
>>>
>>> and if it is an S4 method I think it should be
>>>
>>> \S4method{replacementMethod}{signature_list}(object)<- newValue
>>
>> In the case reported by Marc, replacementMethod was both: a
>> replacement (generic) function and a replacement method. And the
>> man page had an alias for both. Marc replaced
>>
>>   replacementMethod(object) = newValue
>>
>> with
>>
>>   \S4method{replacementMethod}{signature_list}(object)<- newValue
>>
>> and that solved the problem. But replacing '=' with '<-' solves it too.
>>
>> Shouldn't 'R CMD check' treat the 2 assignment operators the same way
>> since they are equivalent?
>>
>
> They are not equivalent (you can't use = in many places where you can use<-).

I tried to lower the chance of getting a comment like this by saying
"the 2 *assignment* operators are equivalent" but apparently I
failed :-/

Seems to me that the places where I can't replace <- by = are exactly
the places where I would be replacing an assignment operator by
something that is not an assignment operator anymore.

>
> Also my understanding is that it is considered bad practice by some to use = as assignment outside of the command prompt (interactive use) -- but opinions vary and I don't want to start a flame war here ;).

I agree with you. I like to be able to directly copy/paste

   a <- foo()

into

   system.time(... paste it here ...)

and press <return> and have it work. But as you said, opinions may
vary...

Anyway, if 'R CMD check' wants to encourage good practice, fine with
me, but then the warning for 'replacementMethod(object) = newValue'
should be something else and also maybe for consistency the code in
the examples and in the vignette should be checked to detect when =
is used instead of <-

Otherwise, 'R CMD check' should just treat

   replacementMethod(object) = newValue

the same way it treats

   replacementMethod(object) <- newValue

Thanks,
H.


>
> Cheers,
> Simon
>
>
>
>> Thanks!
>> H.
>>
>>>
>>> (though the manual suggests using the S3 style, I'm not sure how
>>> literally to take it).
>>>
>>> Duncan Murdoch
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>> --
>> Hervé Pagès
>>
>> Program in Computational Biology
>> Division of Public Health Sciences
>> Fred Hutchinson Cancer Research Center
>> 1100 Fairview Ave. N, M2-B876
>> P.O. Box 19024
>> Seattle, WA 98109-1024
>>
>> E-mail: hpages at fhcrc.org
>> Phone:  (206) 667-5791
>> Fax:    (206) 667-1319
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>


-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M2-B876
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages at fhcrc.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319