Re: [Rd] Reference classes: accessor functions via 'getRefClass(...)$accessors(...)'

From: Romain Francois <romain_at_r-enthusiasts.com>
Date: Wed, 17 Nov 2010 13:19:14 +0100

Le 17/11/10 13:07, Janko Thyson a écrit :
>
> Hi there,
>
>
>
> I'd like to choose between an "static" and "dynamic" access of a reference
> class field, say 'a'.
>
>
>
> myObj<- getRefClass("Blabla")$new()
>
>
>
> Static: myObj$a
>
> Dynamic: myObj$a.get() where the function retrieves the data
> from a database (or some other location), stores it to a buffer and
> optionally updates the static field value 'a'.
>
>
>
> I've set up such a method 'a.get()' where I can actually decide between
> static and dynamic runmode (so the method also wraps the call 'myObj$a' for
> the static runmode).
>
>
>
> Now I saw that setting up such accessor methods (get/set) is already done
> for me if I use 'getRefClass("Blabla")$accessors(.)'. I just don't
> understand what exactly I have to do there, because this results in an
> error: 'getRefClass("Blabla")$accessors("a")'
>
>
>
> Can anyone point me to the correct use of 'getRefClass(.)$accessors(.)'?
>
>
>
> Thanks a lot,
>
> Janko

Hi,

fields can either be data or active binding functionss. See ?makeActiveBinding for some example of active binding functions in their original context.

Here is an example of a reference class that keeps its data in a file.

require( methods )

Foo <- setRefClass( "Foo",

     fields = list(
         file = "character",
         x = function(value){
             if( missing( value ) ){
                 read.table( file )
             } else{
                 write.table( value, file = file )
             }
         }
     )

)

foo <- Foo$new( file="/tmp/iris.txt" )
foo$x <- iris
foo$x

write.table( subset( iris, Petal.Length < 2), file = "/tmp/iris.txt" ) foo$x

Does that help ?

Romain

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Romain Francois
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Received on Wed 17 Nov 2010 - 12:22:31 GMT

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