[R-pkg-devel] Assigning values to fields in Reference Classes

[Per Nyfelt]

I developed a package where reference classes is used a lot. When 
submitting it to CRAN i got the feedback that  i should not use <<- as 
that was "modifying the global environment". That was a misunderstanding 
that was sorted out but before it was, I started to investigate 
alternative ways to assign values to refclass fields. I can it this 
elsewhere since it does not belong.

Thanks,

Per

On 5/11/20 8:58 PM, Bert Gunter wrote:
> What does this have to do with package development? Seems more like a
> query for r-help.
>
> Cheers,
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
> On Mon, May 11, 2020 at 11:27 AM Per Nyfelt <per using alipsa.se> wrote:
>> Hi,
>>
>> I have been playing with alternative ways to assign values to fields in
>> reference classes.
>>
>> Besides the "standard" <<- there are two other ways that also "seems to
>> work". One is using .self$fieldName assigned with <- and the the other
>> one is field(fieldName, value).
>>
>> With regards to the ".self method" (example below): is this a "safe"
>> equivalent to <<- i.e. are these two ways identical in result and
>> possible "side effects"?
>>
>> StandardAssignment <- setRefClass(
>>     Class ="StandardAssignment",
>>     fields = list(
>>       m_attributes = "list"
>>     ),
>>     methods = list(
>>       setAttribute = function(name, value) {
>>         m_attributes[[as.character(name)]] <<- as.character(value)
>>         return(invisible(.self))
>>       },
>>       getAttribute = function(name) {
>>         m_attributes[[name]]
>>       }
>>     )
>> )
>>
>> s1 <- StandardAssignment$new()
>> s1$setAttribute("name", "foo")
>> s1$getAttribute("name")
>>
>> [1] "foo"
>>
>> SelfAssignment <- setRefClass(
>>     Class ="SelfAssignment",
>>     fields = list(
>>       m_attributes = "list"
>>     ),
>>     methods = list(
>>       setAttribute = function(name, value) {
>>         .self$m_attributes[[as.character(name)]] <- as.character(value)
>>         return(invisible(.self))
>>       },
>>       getAttribute = function(name) {
>>         m_attributes[[name]]
>>       }
>>     )
>> )
>>
>> s2 <- SelfAssignment$new()
>> s2$setAttribute("name", "foo")
>> s2$getAttribute("name")
>>
>> [1] "foo"
>>
>>
>> Best regards,
>>
>> Per
>>
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