[R-pkg-devel] Working with connections

[Joshua Ulrich]

On Sun, Aug 9, 2015 at 8:59 AM, Glenn Schultz <glennmschultz at me.com> wrote:
> Hi All,
>
> I use connections to open and close data folders needed by my package.
> After each function closes I get the following warnings (depending on the
> connection that has been opened).
>
> 10: closing unused connection 3
> (/Library/Frameworks/R.framework/Versions/3.2/Resources/library/BondLab/BondData/bondlabMBS4.rds)
>
> Below is the connection function that is related to the above warning:
>
> #------------------------------------------------------------------------------------
>   #' A connection function to BondData calling MBS cusps
>   #'
>   #' Opens a connection to the BondData folder to call MBS cusip data
>   #' @param MBS.id A character string the MBS.id or cusip number current
> MBS.id is supported
>   #' @export
>   MBS <- function(MBS.id = "character"){
>                   MBS.Conn <- gzfile(description = paste(system.file(package
> = "BondLab"),
>                               "/BondData/", MBS.id, ".rds", sep = ""), open
> = "rb")
>                   MBS <- readRDS(MBS.Conn)
>                   return(MBS)
>                   close.connection(MBS.Conn)
>                   }
>
> I have googled this warning and it seems to be triggered when a function
> terminates and the connection is open.  But, I think the connection function
> closes the connection once the object is returned.  What am I doing wrong?
>
Your call to return() exits the function, so the close.connection()
call is never evaluated.  Considering using on.exit() to close the
connection, since it will close the connection regardless of how the
function exits (e.g. because of an error).

> -Glenn
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