The goal of sloop is to provide tools to help you interactively explore and understand object oriented programming in R, particularly with S3.
Please note that unlike other r-lib packages, sloop only works with R 3.3 and later.
You can install sloop from github with:
# install.packages("pak")
pak::pak("r-lib/sloop")
sloop provides a variety of tools for understanding how S3 works. The most useful is probably s3_dispatch(). Given a function call, it shows the set of methods that are considered, found, and actually called:
s3_dispatch(print(Sys.time())) #> => print.POSIXct #> print.POSIXt #> * print.default
To the best of my ability it covers all the details of S3 method dispatch including group generics, internal generics, implicit classes, and use of NextMethod() (indicated by ->):
# Implicit class x <- matrix(1:6, nrow = 2) s3_dispatch(print(x)) #> print.matrix #> print.integer #> print.numeric #> => print.default # Internal generic length.numeric <- function(x) 10 s3_dispatch(length(x)) #> length.matrix #> length.integer #> * length.numeric #> length.default #> => length (internal) s3_dispatch(length(structure(x, class = "numeric"))) #> => length.numeric #> length.default #> * length (internal) # NextMethod s3_dispatch(Sys.Date()[1]) #> => [.Date #> [.default #> -> [ (internal) # group generic + NextMethod() s3_dispatch(sum(Sys.Date())) #> sum.Date #> sum.default #> => Summary.Date #> Summary.default #> -> sum (internal)
It also provides tools for determing what type of function or object you’re dealing with:
ftype(t) #> [1] "S3" "generic" ftype(t.test) #> [1] "S3" "generic" ftype(t.data.frame) #> [1] "S3" "method" otype(1:10) #> [1] "base" otype(mtcars) #> [1] "S3" otype(R6::R6Class()$new()) #> [1] "R6"
And for retrieving the methods associated with a generic or class:
s3_methods_class("factor")
#> # A tibble: 28 × 4
#> generic class visible source
#> <chr> <chr> <lgl> <chr>
#> 1 [ factor TRUE base
#> 2 [[ factor TRUE base
#> 3 [[<- factor TRUE base
#> 4 [<- factor TRUE base
#> 5 all.equal factor TRUE base
#> 6 as.character factor TRUE base
#> 7 as.data.frame factor TRUE base
#> 8 as.Date factor TRUE base
#> 9 as.list factor TRUE base
#> 10 as.logical factor TRUE base
#> # ℹ 18 more rows
s3_methods_generic("summary")
#> # A tibble: 39 × 4
#> generic class visible source
#> <chr> <chr> <lgl> <chr>
#> 1 summary aov TRUE stats
#> 2 summary aovlist FALSE registered S3method
#> 3 summary aspell FALSE registered S3method
#> 4 summary check_packages_in_dir FALSE registered S3method
#> 5 summary connection TRUE base
#> 6 summary data.frame TRUE base
#> 7 summary Date TRUE base
#> 8 summary default TRUE base
#> 9 summary ecdf FALSE registered S3method
#> 10 summary factor TRUE base
#> # ℹ 29 more rows
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