[Rd] Surprising behavior when using the reference class with the dollar symbol

[Duncan Murdoch]

On 27/03/2021 10:16 a.m., Jiefei Wang wrote:
> Hi all,
> 
> I'm trying to get the field value of a reference object by the field name,
> but the dollar symbol behaves quite unusual. See example below
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> *.foo <- setRefClass(    "foo",    fields = list(        a = "integer"
> ))x <- .foo$new(a=1L)## This is OKx$a## This is OK`$`(x, "a")## But this is
> not OKi <- "a"`$`(x, i)*

This is really hard to read.  Please post it again, but don't use HTML.

Duncan Murdoch

> 
> For the last line of code I get this error
> 
> 
> *Error in envRefInferField(x, what, getClass(class(x)), selfEnv) :   ‘i’ is
> not a valid field or method name for reference class “foo”*
> 
> It looks like when calling the dollar symbol using the function format, it
> treats the input argument as a character literal and does not evaluate it
> inside the function. I know we have the function `field` to get the slot
> variable, but I wonder if this is designed on purpose as the above example
> works for both list and S4 system.
> 
> Best,
> Jiefei
> 
> 	[[alternative HTML version deleted]]
> 
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