I think it might be useful to have the possibility of passing a function to scale names like so:

library(ggplot2)

df <- expand.grid(X1 = 1:10, X2 = 1:10)
df$value <- df$X1 * df$X2
p1 <- ggplot(df, aes(X1, X2)) + geom_tile(aes(fill = value))

p1 + scale_fill_continuous(function(x) base::toupper(x))

# With function shorthand
p1 + scale_fill_continuous(~ base::toupper(.x))

^{Created on 2021-01-11 by the reprex package (v0.3.0)}

Something like this would make code snippets more portable. In my case, I have a function that makes a plot and I had to define the title outside the plot depending on the function arguments. With this, I could've defined a global dictionary which translates column names to actual (human readable) variable names and re-use that all over my report.

To produce the code above I just added this

  if (is.formula(name)) {
    name <- as_function(name)
  }

  if (is.function(name)) {
    make_title <- name
    name <- waiver()
  } else {
    make_title <- super$make_title
  }

before this line:

https://github.com/tidyverse/ggplot2/blob/master/R/scale-.r#L107

And then added make_title = make_title to the ggproto construction.

All tests pass, so changing this should be safe.