[Rd] Reference Classes copy(shallow=FALSE) unexpected behavior.

[John Chambers]

Good suggestion for this case.

But the general problem is tricky.  What about reference objects 
contained in attributes or slots of other objects, etc?  What is  needed 
for total copying is a switch in the low-level duplication code that 
says to copy reference objects.  It's also possible that one does NOT 
want all such objects copied.

For now, it may be that specialized copy() methods are needed for 
classes that have subsidiary reference objects inside non-reference objects.

John

On 5/11/11 6:37 AM, Hadley Wickham wrote:
> Hi Manuel,
>
> The source code for copy is short and pretty readable, so I'd
> encourage you to look at it:
>
>> setRefClass("XXX")$copy
> Class method definition for method copy()
> function (shallow = FALSE)
> {
>      def<- .refClassDef
>      value<- new(def)
>      vEnv<- as.environment(value)
>      selfEnv<- as.environment(.self)
>      for (field in names(def at fieldClasses)) {
>          if (shallow)
>              assign(field, get(field, envir = selfEnv), envir = vEnv)
>          else {
>              current<- get(field, envir = selfEnv)
>              if (is(current, "envRefClass"))
>                  current<- current$copy(FALSE)
>              assign(field, current, envir = vEnv)
>          }
>      }
>      value
> }
>
> The basic problem is that you have a list of reference class objects,
> and currently copy does not recurse into lists.  I think this could be
> fixed with
>
> deep_copy<- function(x) {
>    if (is(current, "envRefClass")) {
>      x$copy()
>    } else if (is.list(x))
>      lapply(x, deep_copy)
>    } else {
>      x
>    }
> }
>
> function (shallow = FALSE){
>      def<- .refClassDef
>      value<- new(def)
>      vEnv<- as.environment(value)
>      selfEnv<- as.environment(.self)
>      for (field in names(def at fieldClasses)) {
>          if (shallow)
>              assign(field, get(field, envir = selfEnv), envir = vEnv)
>          else {
>              current<- get(field, envir = selfEnv)
>              assign(field, deep_copy(current), envir = vEnv)
>          }
>      }
>      value
> }
>
> Hadley
>
> 2011/5/11 Manuel Castejón Limas<manuel.castejon at unileon.es>:
>> Dear Hadley,
>>
>> Thank you very much for your interest in the question proposed.
>> The Con class is a Reference Class. P and k are from class listCon.
>>
>> I provide in the following lines a little more detail in order to be able
>> to reproduce the case.
>>
>> #Class declaration
>> gCon<- setRefClass("Con", fields=list(from="ANY",weight="numeric"))
>> gListAMORE<- setRefClass("listAMORE", fields=list(.Data="list"))
>> gListCon<- setRefClass("listCon", contains="listAMORE")
>>
>> # Let's create a few connections
>> con1<- gCon$new(from=1, weight=1.1)
>> con2<- gCon$new(from=2, weight=2.2)
>> con3<- gCon$new(from=3, weight=3.3)
>>
>> # And a list of connections
>> lcon<-gListCon$new()
>> lcon$.Data<- list(con1, con2, con3)
>>
>> # At this point, lcon contains:
>> lcon$.Data
>> [[1]]
>> An object of class "Con"
>> <environment: 0x9a1534>
>>
>> [[2]]
>> An object of class "Con"
>> <environment: 0xcd7ff0>
>>
>> [[3]]
>> An object of class "Con"
>> <environment: 0xdca724>
>>
>> # Let's copy lcon to k
>> k<- lcon$copy(shallow=FALSE)
>>
>> # Now k is a new object but the cons are shared with lcon!
>> k$.Data
>> [[1]]
>> An object of class "Con"
>> <environment: 0x9a1534>
>>
>> [[2]]
>> An object of class "Con"
>> <environment: 0xcd7ff0>
>>
>> [[3]]
>> An object of class "Con"
>> <environment: 0xdca724>
>>
>>
>> Best regards
>>
>> Manuel
>>
>>
>>
>> El 11/05/11 14:00, "Hadley Wickham"<hadley at rice.edu>  escribió:
>>
>>> 2011/5/10 Manuel Castejón Limas<manuel.castejon at unileon.es>:
>>>> Dear all,
>>>>
>>>> I've just discovered the 'Reference Classes'.
>>>> In a previous attempt ---a year ago--- to re-implement in a Object
>>>> Oriented
>>>> fashion the AMORE package using S4 classes I strongly felt the need of
>>>> such
>>>> capability. It's great to have the Reference Classes now available.
>>>> Along
>>>> with the discovery of the Rcpp package, this new programming paradigm
>>>> has
>>>> boosted my interest in rewriting that package.
>>>>
>>>> Nevertheless, I have found a surprising behavior in the
>>>> $copy(shallow=FALSE)
>>>> method. Let's have a look at the results which I believe are
>>>> self-explanatories. The ".Data" field is a list which contains objects
>>>> from
>>>> the "Con" class  ---connections for what is worth---.
>>>
>>> What sort of class is the Con class? S4 or reference?
>>>
>>> Hadley
>>>
>>>
>>> --
>>> Assistant Professor / Dobelman Family Junior Chair
>>> Department of Statistics / Rice University
>>> http://had.co.nz/
>>>
>>
>>
>>
>>
>
>
>