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

Jiefei Wang @zwj|08 @end|ng |rom gm@||@com
Sat Mar 27 15:16:54 CET 2021

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

*.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)*

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.


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