R help - Feb 2003 - `UNPROTECT' and `return'

Dear R experts,

In all R functions written in C one must unprotect
result before returning them:

  {
      ...
      UNPROTECT(1)  /* unprotecting `ans' */

      return ans;
  }

Why does one shure that memory occupied by `ans'
won't be used by R immediately after unprotecting?

Ok, is the next construction also absolutely safe?
  {
      ...
      UNPROTECT(1)  /* unprotecting `ans' */

      PROTECT( val = ans )
      ...
  }

Thanks a lot!


--
WBR,
Timur.

This _is_ covered in `Writing R Extensions'.  What is unsafe is to allow a 
gc to occur.

On Wed, 12 Feb 2003, Timur Elzhov wrote:
> In all R functions written in C one must unprotect
> result before returning them:
> 
>   {
>       ...
>       UNPROTECT(1)  /* unprotecting `ans' */
> 
>       return ans;
>   }
> 
> Why does one shure that memory occupied by `ans'
> won't be used by R immediately after unprotecting?
> 
> Ok, is the next construction also absolutely safe?
>   {
>       ...
>       UNPROTECT(1)  /* unprotecting `ans' */
> 
>       PROTECT( val = ans )
>       ...
>   }
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595