How to access original expression that is passed to an overwritten generic in R?

Question

I want to overwrite the plot method for a certain class. I want the expression string to be used as the axis label. However it seems that the method dispatch somehow evaluates the expression so I can't retrieve the original expression the way I expected(sorry if I am using the wrong vocabulary here). In the following a minimal example:

library(rlang)

make_s = function(x) structure(x, class = "s")


plot2= function(x) print(enexpr(x))
plot.s = function(x) print(enexpr(x))

variable_name = make_s(1)
plot2(variable_name)
#Output:
#variable_name
plot(variable_name)
#Output:
#[1] 1
#attr(,"class")
#[1] "s"

My expectation was that plot.s returns "variable_name" which it doesn't. Why is that and how to remedy this?

Answer 1

That appears to be a bug or misuse of the rlang::enexpr function. I don't know that function (and its docs are the usual tidyverse mishmash of made up words without any real explanation), so here's the base way to do what you want:

make_s = function(x) structure(x, class = "s")

plot.s = function(x) print(deparse1(substitute(x)))

variable_name = make_s(1)
plot(variable_name)
#> [1] "variable_name"

^{Created on 2023-12-15 with reprex v2.0.2}