R devel - Nov 2010 - Reference classes: accessor functions via 'getRefClass(...)$accessors(...)'

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


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Le 17/11/10 13:07, Janko Thyson a ?crit :
>
> 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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"Janko Thyson" <janko.thyson at ku-eichstaett.de> writes:
> 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(.)'?
It works for me:

X <- setRefClass("XXX", fields = list(a = "character"))
X$accessors("a")
X
# ...
# Class Methods:  
#    "callSuper", "export", "getA",
"import", "initFields", "setA"
# ...

accessors() convenience method creates setA and getA functions:

x <- X$new()
x$getA
#Class method definition for method getA()
#function () 
#a
#<environment: 02a198c0>

HTH,
Vitalie.
> 
>
> Thanks a lot,
>
> Janko
>
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