[Rd] How to assign NULL value to pairlist element while keeping it a pairlist?

[Michael Lawrence]

Hi Henrik,

It would help to understand your use case for pairlists.

Thanks,
Michael

On Wed, Oct 12, 2016 at 9:40 AM, Michael Lawrence <michafla at gene.com> wrote:
> The coercion is probably the most viable workaround for now, as it's
> consistent with what happens internally for calls. All pairlists/calls
> are converted to list for subassignment, but only calls are converted
> back. My guess is that the intent was for users to move from using a
> pairlist to the "new" (almost 20 years ago) list. In my opinion,
> consistency trumps "convenience" in this case. If others agree, I'll
> change it to also coerce back to pairlist.
>
> Michael
>
> On Wed, Oct 12, 2016 at 9:20 AM, Henrik Bengtsson
> <henrik.bengtsson at gmail.com> wrote:
>> Hi, I seem to not be able to assign NULL to an element of a pairlist
>> without causing it to be coerced to a plain list.  For example:
>>
>>> x <- pairlist(1, 2)
>>> class(x)
>> [1] "pairlist"
>>
>>> x[1] <- list(NULL)
>>> class(x)
>> [1] "list"
>>
>> This actually true for all [()<- assignments regardless of list value, e.g.
>>
>>> x <- pairlist(1, 2)
>>> x[1] <- list(0)
>> [1] "list"
>>
>> I also tried assigning a pairlist(), but still the same problem:
>>
>>> x <- pairlist(1, 2)
>>> x[1] <- pairlist(0)
>> [1] "list"
>>
>> The only workaround I'm aware of is to:
>>
>> x <- as.pairlist(x)
>>
>> at the end.  Any other suggestions?
>>
>> Thanks,
>>
>> Henrik
>>
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