[Rd] Rubbish values written with zero-length vectors (PR#14217)

[Peter Dalgaard]

OK. I now have a version which seems to do the trick and reuses an 
existing error message. Will commit to r-devel if and when make 
check-devel succeeds.

-p

Peter Dalgaard wrote:
> seth at userprimary.net wrote:
> 
> Thanks, Seth. Martin Morgan sent a patch for a few lines above yours, 
> which I didn't have a chance to review until now:
> 
> -   if (!isVectorList(x) && LENGTH(y) > 1)
> -       error(_("more elements supplied than there are to replace"));
> +   if (!isVectorList(x) && LENGTH(y) != 1)
> +       if (LENGTH(y) == 0)
> +           error(_("fewer elements supplied than there are to replace"));
> +       else
> +           error(_("more elements supplied than there are to replace"));
> 
> I _think_ that you are both right that there is no way for a zero-length 
> RHS not to be an error. E.g.,
> 
>  > x[[0]] <- real(0)
> Error in x[[0]] <- real(0) : attempt to select less than one element
> 
> The difference between Seth's solution and Martin's is whether to 
> pre-check for nsubs==1, and I don't think we want that because of
> 
>  > x <- matrix(1:4,2,2)
>  > x[[2,2]]
> [1] 4
>  > x[[2,2]] <- integer(0)
>  > x
>      [,1]      [,2]
> [1,]    1         3
> [2,]    2 142000760
> 
> 
>> On 2/20/10 7:50 AM, Peter Dalgaard wrote:
>>> You don't want to understand, believe me! ;-)
>>>
>>> It's a bug, probably not the very worst kind, but accessing memory that
>>> isn't yours is potentially harmful (but writing to it is considerably
>>> worse).
>>>
>>> Looks like the issue only concerns the right hand side; nothing to do
>>> with the auto-expansion of v. I also get
>>>
>>>> v <- integer(0)
>>>> u <- integer(1)
>>>> u[[2]] <-v
>>>> u
>>> [1]         0 142000760
>>>> u[[1]] <-v
>>>> u
>>> [1] 142000760 142000760
>>>> a <- 1
>>>> a[[1]] <-v
>>>> a
>>> [1] 142000760
>>
>> I'm thinking this should be an error.  Similar to:
>>
>>> v = 1
>>> v[[1]] = integer(3)
>> Error in v[[1]] = integer(3) :
>>   more elements supplied than there are to replace
>>
>> But instead not enough elements supplied.  Perhaps:
>>
>>> v[[1]] = integer()
>> Error in v[[1]] = integer() : [[ ]] replacement has zero length
>>
>> The code in do_subassign2_dflt currently does not check that the
>> replacement has length > 0 for the nsubs == 1 case.  I think we want:
>>
>>
>> @@ -1529,6 +1532,8 @@ do_subassign2_dflt(SEXP call, SEXP op, SEXP args,
>> SEXP rho)
>>         if (nsubs == 0 || CAR(subs) == R_MissingArg)
>>             error(_("[[ ]] with missing subscript"));
>>         if (nsubs == 1) {
>> +            if (length(y) == 0)
>> +                error(_("[[ ]] replacement has zero length"));
>>             offset = OneIndex(x, thesub, length(x), 0, &newname,
>> recursed ? len-1 : -1, R_NilValue);
>>             if (isVectorList(x) && isNull(y)) {
>>                 x = DeleteOneVectorListItem(x, offset);
>>
>>
>> + seth
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
> 
> 


-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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