R devel - Apr 2011 - Invalid connection after closing?

Dear all,

I do not completely understand following behaviour :
> con <- file("test.txt")
> isOpen(con)
[1] FALSE
> open(con)
> isOpen(con)
[1] TRUE
> close(con)
> isOpen(con)
Error in isOpen(con) : invalid connection
> str(con)
Classes 'file', 'connection'  atomic [1:1] 3
  ..- attr(*, "conn_id")=<externalptr>

Why do I get an error, indicating an invalid connection, after I
closed a connection? Is this to be expected?
Cheers
Joris

-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
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On 08/04/2011 10:56 AM, Joris Meys wrote:
> Dear all,
>
> I do not completely understand following behaviour :
>
> >  con<- file("test.txt")
> >  isOpen(con)
> [1] FALSE
> >  open(con)
> >  isOpen(con)
> [1] TRUE
> >  close(con)
> >  isOpen(con)
> Error in isOpen(con) : invalid connection
> >  str(con)
> Classes 'file', 'connection'  atomic [1:1] 3
>    ..- attr(*, "conn_id")=<externalptr>
>
> Why do I get an error, indicating an invalid connection, after I
> closed a connection? Is this to be expected?
Quoting ?close: " ?close? closes and destroys a connection. " In the 
current implementation, connections are a finite resource, and you need 
to be able to get rid of them when you are done. close(con) is the way 
to do that. If you want to re-open it, you need to remember the filename 
(or extract it before calling close()), and issue another call to file().

Duncan Murdoch