Automatic printing (show method) not working for S7 classes

[atsyplenkov]

When creating a class with S7, there doesn't seem to be a way to implement automatic printing behavior when the object is typed in the console, unlike S4 classes.

Is it a limitation of S7 or is there any workaround I am missing?

Minimal Reproducible Example

library(S7)

# Define a simple class
Track <- new_class(
  "Track",
  properties = list(
    x = class_numeric,
    y = class_numeric
  )
)

# Create an instance
t1 <- Track(
  x = 1:3,
  y = c(1, 4, 9)
)

# Current behavior: prints internal representation
t1
#> <Track>
#>  @ x: int [1:3] 1 2 3
#>  @ y: num [1:3] 1 4 9

# Attempted solutions that didn't work:

# 1. Using S7 method for show
show <- new_generic("show", "x")
method(show, Track) <- function(x) {
  print(c(
    x = max(x@x),
    y = min(x@y)
  ))
}

#  prints internal representation
t1
#> <Track>
#>  @ x: int [1:3] 1 2 3
#>  @ y: num [1:3] 1 4 9

# Prints desired representation
show(t1)
#>  x  y 
#> 3  1

#2. Trying to bridge with S4
setClass("Track", 
         slots = c(x = "numeric", y = "numeric"),
         contains = "S7_object")

setMethod("show", "Track",
  function(object) {
    print(c(
      x = max(object@x),
      y = min(object@y)
    ))
  }
)

# None of these approaches achieve the desired automatic printing behavior
t1
#> <Track>
#>  @ x: int [1:3] 1 2 3
#>  @ y: num [1:3] 1 4 9

^{Created on 2024-12-24 with reprex v2.1.0}

Expected Behavior

When typing t1 in the console, it should display a custom formatted output (similar to how S4 classes work with show methods).

setClass("Track", slots = c(x = "numeric", y = "numeric"))

setMethod("show", "Track",
  function(object) {
    print(c(
      x = max(object@x),
      y = min(object@y)
    ))
  }
)

t1 <- new("Track", x=1:20, y=(1:20)^2)
t1
#>  x  y 
#> 20  1

^{Created on 2024-12-24 with reprex v2.1.0}

Show Session Info

library(S7)
sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R version 4.4.2 (2024-10-31 ucrt)
#>  os       Windows 10 x64 (build 19045)
#>  system   x86_64, mingw32
#>  ui       RTerm
#>  language (EN)
#>  collate  English_United States.utf8
#>  ctype    English_United States.utf8
#>  tz       Pacific/Auckland
#>  date     2024-12-24
#>  pandoc   3.2 @ c:\\scoop\\apps\\positron\\2025.01.0-39\\resources\\app\\quarto\\bin\\tools/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date (UTC) lib source
#>  cli           3.6.3   2024-06-21 [1] RSPM
#>  digest        0.6.35  2024-03-11 [1] CRAN (R 4.4.1)
#>  evaluate      1.0.1   2024-10-10 [1] RSPM (R 4.4.0)
#>  fastmap       1.1.1   2023-02-24 [1] CRAN (R 4.4.1)
#>  fs            1.6.4   2024-04-25 [1] CRAN (R 4.4.1)
#>  glue          1.8.0   2024-09-30 [1] RSPM
#>  htmltools     0.5.8.1 2024-04-04 [1] CRAN (R 4.4.1)
#>  knitr         1.49    2024-11-08 [1] RSPM
#>  lifecycle     1.0.4   2023-11-07 [1] CRAN (R 4.4.1)
#>  magrittr      2.0.3   2022-03-30 [1] CRAN (R 4.4.1)
#>  purrr         1.0.2   2023-08-10 [1] CRAN (R 4.4.1)
#>  R.cache       0.16.0  2022-07-21 [1] CRAN (R 4.4.1)
#>  R.methodsS3   1.8.2   2022-06-13 [1] CRAN (R 4.4.0)
#>  R.oo          1.26.0  2024-01-24 [1] CRAN (R 4.4.0)
#>  R.utils       2.12.3  2023-11-18 [1] CRAN (R 4.4.1)
#>  reprex        2.1.0   2024-01-11 [1] CRAN (R 4.4.1)
#>  rlang         1.1.4   2024-06-04 [1] CRAN (R 4.4.1)
#>  rmarkdown     2.29    2024-11-04 [1] RSPM
#>  S7          * 0.2.0   2024-11-07 [1] RSPM
#>  sessioninfo   1.2.2   2021-12-06 [1] CRAN (R 4.4.1)
#>  styler        1.10.3  2024-04-07 [1] CRAN (R 4.4.1)
#>  vctrs         0.6.5   2023-12-01 [1] CRAN (R 4.4.1)
#>  withr         3.0.2   2024-10-28 [1] RSPM
#>  xfun          0.49    2024-10-31 [1] RSPM (R 4.4.0)
#>  yaml          2.3.10  2024-07-26 [1] RSPM (R 4.4.0)
#> 
#>  [1] C:/Users/TsyplenkovA/AppData/Local/R/win-library/4.4
#>  [2] C:/Program Files/R/R-4.4.2/library
#> 
#> ──────────────────────────────────────────────────────────────────────────────

[hadley]

Try providing a method for the S3 print generic.