[R-pkg-devel] [External] SETLENGTH()

[Vladimir Dergachev]

On Sat, 4 May 2024, luke-tierney using uiowa.edu wrote:

> On Sat, 4 May 2024, Vladimir Dergachev wrote:
>
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>> 
>> I noticed a note on RMVL package check page for development version of R:
>> 
>> Found non-API call to R: ?SETLENGTH?
>> 
>> Is this something that is work-in-progress for the development version, or
>> has SETLENGTH() been deprecated ? What should I use instead ?
>
> SETLENGTH has never been part of the API. It is not safe to use except
> in a very, very limited set of circumstances. Using it in other
> settings will confuse the memory manager, leading at least to
> mis-calculation of memory use information and possibly to
> segfaults. For most uses I have seen, copying to a new vector of the
> right size is the only safe option.
>
> The one context where something along these lines might be OK is for
> growable vectors. This concept is emphatically not in the API at this
> point, and the way it is currently implemented in base is not robust
> enough to become an API (even though some packages have used it). It
> is possible that a proper API for this will be added; at that point
> SETLENGTH will be removed from the accessible entry points on
> platforms that allow this.
>
> So if you are getting a note about SETLENGTH, either stop using it or
> be prepared to make some changes at fairly short notice.
>
> [Similar considerations apply to SET_TRUELENGT. In most but not all
> cases using it is less dangerous, but you should still look for other
> options if you want your code to continue to work.]

Great, thank you for the explanation ! I will rewrite the code to not use 
SETLENGTH().

My use case was to allocate a vector of some size N_max and then 
repeatedly populate it with variable number of elements. Since the vector 
was protected during the loop, I would have expected to save on memory 
allocation calls.

best

Vladimir Dergachev

>
> Best,
>
> luke
>
>> 
>> thank you very much
>> 
>> Vladimir Dergachev
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>> 
>
> -- 
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
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>