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.
Usage
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:
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: 27 x 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
#> # … with 17 more rows
s3_methods_generic("summary")
#> # A tibble: 40 x 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
#> # … with 30 more rows
