[Rd] strange increase in the reference number
brod|e@g@@|@m @end|ng |rom y@hoo@com
Sat Jul 13 19:42:50 CEST 2019
If you would like more details I wrote about this recently:
Basically as soon as you hit a closure R assumes that theargument might still have a surviving reference to iteven after the closure evaluation ends because theclosure environment still exists. This is why thenamed count is set to the maximum value.
Note that since the time I wrote the above andnow the maximum reference count changed to 7 from 3. Atsome point I believe there was a plan to add true(er?)reference counting in 3.6 to but that was not quiteready in time.
On Friday, July 12, 2019, 2:47:41 PM EDT, Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
On 12/07/2019 1:22 p.m., King Jiefei wrote:
> I just found a strange increase in the reference number and I'm wondering
> if there is any reason for it, here is the code.
> @0x000000001bf0b9b0 14 REALSXP g0c3 [NAM(1)] (len=3, tl=0) 1,2,3
>  TRUE
> @0x000000001bf0b9b0 14 REALSXP g0c3 [NAM(7)] (len=3, tl=0) 1,2,3
> The variable *a* initially has one reference number, after calling
> *is.vector* function, the reference number goes to 7, which I believe is
> the highest number that is allowed in R. I also tried the other R
> functions, *is.atomic, is.integer* and *is.numeric* do not increase the
> reference number, but *typeof *will do. Is it intentional?
is.vector() is a closure that calls .Internal. is.atomic(),
is.integer() and is.numeric() are all primitives.
Generally speaking closures that call .Internal are easier to implement
(e.g. is.vector can use the regular mechanism to set a default for its
second argument), but less efficient in CPU time. From it's help page,
it appears that the logic for is.vector() is a lot more complex than for
the others, so that implementation does make sense.
So why does NAMED go to 7? Initially, the vector is bound to a. Within
is.vector, it is bound to the local variable x. At this point there are
two names bound to the same object, so it has to be considered
immutable. There's really no difference between any of the values of 2
or more in the memory manager. (But see
http://developer.r-project.org/Refcnt.html for some plans. That
document is from about 5 years ago; I don't know the current state.)
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