combine UserDefinedDatabase and regular environments

On Thu, Nov 19, 2009 at 10:54 AM, Romain Francois
<romain.francois at dbmail.com <mailto:romain.francois at dbmail.com>> wrote:

    On 11/19/2009 06:14 PM, Michael Lawrence wrote:



        On Thu, Nov 5, 2009 at 9:58 AM, Romain Francois
        <romain.francois at dbmail.com <mailto:romain.francois at dbmail.com>
        <mailto:romain.francois at dbmail.com
        <mailto:romain.francois at dbmail.com>>> wrote:

            Hello,

            Is it possible to have the effect of UserDefinedDatabase
        outside of
        "attached" environments ? Can I disguise an environment of the
            sys.frames() as a UserDefinedDatabase ?

            This seems to suggest that it might be possible :

         > f <- function(){ e <- environment(); class(e) <-

        "UserDefinedDatabase"; ff }

         > f()

        The UserDefinedDatabase support expects an R_ObjectTable C structure
        embedded within an externalptr as the HASHTAB of the environment. So
        it's really only possible from C.


    Sure. Too bad both environments and user defined database use
    HASHTAB with completely different meanings.

    What I would want is something like this:

    f <- function(){
            attachLocally( getSomeUserDefinedDatabaseFromC()  )
            HELLO
    }

    and the variable associated with the binding "HELLO" would come
    dynamically from the user defined database.


    A more concrete example : rJava now has javaImport, that combined
    with attach allows dynamic lookup for class names within a set of
    imported java package paths:

    attach( javaImport( "java.util" ), name = "java:java.util" )
    v <- new( Vector )
    m <- new( HashMap )

    This is nice, but then as usual with attach, you forget to detach,
    ... this question is about to find a way to have this instead:

    f <- function(){
            import( "java.util" )
            v <- new( Vector )
            v$add( 1 )
            v
    }

    where the "java.util" is no more looked up when f returns.



Probably no clean way to accomplish that. But you could always use
with() if you can get that Java package as an environment.

Or use
environment<-() to enclose your function in it. That's actually fairly
Java-like, as normally the import has file scope and your classes are
enclosed within that file.

Michael