Illustrate S3 dispatch — s3

s3_dispatch() prints a list of all possible function names that will be considered for method dispatch. There are four possible states:

=> method exists and is found by UseMethod().
-> method exists and is used by NextMethod().
* method exists but is not used.
Nothing (and greyed out in console): method does not exist.

Learn more at https://adv-r.hadley.nz/s3.html.

Usage

s3_dispatch(call, env = parent.frame())

Arguments

call: Example call to S3 method
env: Environment in which to evaluate call

Examples

x <- Sys.time()
s3_dispatch(print(x))
#> => print.POSIXct
#>    print.POSIXt
#>  * print.default
s3_dispatch(is.numeric(x))
#>    is.numeric.POSIXct
#> => is.numeric.POSIXt
#>    is.numeric.default
#>  * is.numeric (internal)
s3_dispatch(as.Date(x))
#> => as.Date.POSIXct
#>    as.Date.POSIXt
#>  * as.Date.default
s3_dispatch(sum(x))
#>    sum.POSIXct
#>    sum.POSIXt
#>    sum.default
#> => Summary.POSIXct
#>    Summary.POSIXt
#>    Summary.default
#> -> sum (internal)

# Internal vs. regular generic
x1 <- 1
x2 <- structure(2, class = "double")

my_length <- function(x) UseMethod("my_length")
s3_dispatch(my_length(x1))
#>    my_length.double
#>    my_length.numeric
#>    my_length.default
s3_dispatch(my_length(x2))
#>    my_length.double
#>    my_length.default

length.double <- function(x) 10
s3_dispatch(length(x1))
#>  * length.double
#>    length.numeric
#>    length.default
#> => length (internal)
s3_dispatch(length(x2))
#> => length.double
#>    length.default
#>  * length (internal)