[Rd] PROTECT help

[Terry Therneau]

Brian & Duncan:
   Thanks.  This was exactly what I needed to know.

Terry

On 03/27/2012 08:41 AM, Prof Brian Ripley wrote:
> On 27/03/2012 14:22, Terry Therneau wrote:
>> I received the following note this AM. The problem is, I'm not quite
>> sure how to fix it.
>> Can one use PROTECT(coxlist(eval(PROTECT.... , do I create an
>> intermediate variable, or otherwise?
>
> You can, but I find it easiest to follow if you create an intermediate 
> variable.  Look for example at unique.c:
>
>             SEXP call, r;
>             PROTECT(call = lang2(install("as.character"), s));
>             PROTECT(r = eval(call, env));
>             UNPROTECT(2);
>             return r;
>
>
>
>>
>> I'm willing to update the code if someone will give me a pointer to the
>> right documentation. This particular chunk was written when there was a
>> lot of change going on in the callback mechanism and so there might be a
>> safer and/or simpler and/or more standard aproach by now. The routine in
>> question has to do with penalized Cox models, the C code needs to get
>> the value of the penalty and the penalty is an arbitrary S expression
>> passed down from top level.
>>
>> Terry T
>>
>> ----------------------------
>>
>> In survival_2.36-12 (and earlier), in the function cox_callback() at
>> cox_Rcallback.c:40:
>>
>> PROTECT(coxlist=eval(lang2(fexpr,data),rho));
>>
>> the return value of the call to lang2() is vulnerable if allocations
>> within eval() give rise to garbage collection.
>>
>> (Discovered during CXXR development.)
>>
>> Andrew
>>
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>
>