[Rd] question about assignment warnings for replacement methods

[Simon Urbanek]

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 <-).

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 ;).

Cheers,
Simon



> Thanks!
> H.
> 
>> 
>> (though the manual suggests using the S3 style, I'm not sure how
>> literally to take it).
>> 
>> Duncan Murdoch
>> 
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> 
> 
> -- 
> Hervé Pagès
> 
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