Unused argument when defining custom `update_ggplot` method

[jtlandis]

I found a strange issue with using update_ggplot through + method.

I expected for it to be easy to add custom objects to any ggplot object with update_ggplot method but it seems like when using the + method, the latter object is not used?

Here is the code to reproduce the bug:

library(S7)
library(ggplot2)

# simple class to apply a function to a ggplot object
mod_gg <- new_class(
  "mod_gg",
  S7_object,
  properties = list(
    action = class_function
  )
)

method(update_ggplot, list(mod_gg, class_ggplot)) <-
  function(object, plot) {
    object@action(plot)
  }

# finds all text layers and rotates angle by 90
rotate_text_labels <- function(plot) {
  layers <- plot@layers
  is_text <- grepl("text", x = names(layers))
  layers[is_text] <- lapply(
    layers[is_text],
    function(layer) {
      new_layer <- ggproto(NULL, layer)
      new_layer$aes_params$angle <- (new_layer$aes_params$angle %||% 0) + 90
      new_layer
    }
  )
  plot@layers <- layers
  plot
}

p <- ggplot(NULL) +
  geom_text(aes(x = 1, y = 1), label = "Hello World!")
mod <- mod_gg(rotate_text_labels)

p

p + mod
#> Error in `method(update_ggplot, list(mod_gg, ggplot2::ggplot))`(object = <object>, : unused argument ("mod")
update_ggplot(mod, p)

utils::sessionInfo()
#> R version 4.5.0 (2025-04-11)
#> Platform: aarch64-apple-darwin20
#> Running under: macOS Sequoia 15.6.1
#> 
#> Matrix products: default
#> BLAS:   /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRblas.0.dylib 
#> LAPACK: /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.12.1
#> 
#> locale:
#> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
#> 
#> time zone: America/New_York
#> tzcode source: internal
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] ggplot2_4.0.0 S7_0.2.0     
#> 
#> loaded via a namespace (and not attached):
#>  [1] vctrs_0.6.5        cli_3.6.5          knitr_1.50         rlang_1.1.6       
#>  [5] xfun_0.53          generics_0.1.4     labeling_0.4.3     glue_1.8.0        
#>  [9] htmltools_0.5.8.1  scales_1.4.0       rmarkdown_2.29     grid_4.5.0        
#> [13] tibble_3.3.0       evaluate_1.0.5     fastmap_1.2.0      yaml_2.3.10       
#> [17] lifecycle_1.0.4    compiler_4.5.0     dplyr_1.1.4        fs_1.6.6          
#> [21] RColorBrewer_1.1-3 pkgconfig_2.0.3    farver_2.1.2       digest_0.6.37     
#> [25] R6_2.6.1           tidyselect_1.2.1   reprex_2.1.1       pillar_1.11.0     
#> [29] magrittr_2.0.4     tools_4.5.0        withr_3.0.2        gtable_0.3.6

^{Created on 2025-09-24 with reprex v2.1.1}

[teunbrand]

Note that update_ggplot() has ... as an argument, that will be passed a name for the object. If your method does not include ..., it will be passed more arguments than it can handle.

[jtlandis]

That seemed to be the issue, thanks! I'll go ahead and close it.

I thought that S7::`method<-` used to output a warning if the formals didn't match the generic - my bad for not double checking.

[teunbrand]

output a warning if the formals didn't match the generic

This seems like a sensible thing to do honestly