Register a method for a suggested dependency
Generally, the recommend way to register an S3 method is to use the
S3Method() namespace directive (often generated automatically by the
@export roxygen2 tag). However, this technique requires that the generic
be in an imported package, and sometimes you want to suggest a package,
and only provide a method when that package is loaded. s3_register()
can be called from your package's .onLoad() to dynamically register
a method only if the generic's package is loaded. (To avoid taking a
dependency on vctrs for this one function, please feel free to copy
and paste the function source into your own package.)
.s3register(generic, class, method = NULL)
generic |
Name of the generic in the form |
class |
Name of the class |
method |
Optionally, the implementation of the method. By default,
this will be found by looking for a function called Note that providing |
For R 3.5.0 and later, s3_register() is also useful when demonstrating
class creation in a vignette, since method lookup no longer always involves
the lexical scope. For R 3.6.0 and later, you can achieve a similar effect
by using "delayed method registration", i.e. placing the following in your
NAMESPACE file:
if (getRversion() >= "3.6.0") {
S3method(package::generic, class)
}nothing; called for side effects
# A typical use case is to dynamically register tibble/pillar methods
# for your class. That way you avoid creating a hard dependency on packages
# that are not essential, while still providing finer control over
# printing when they are used.
.onLoad <- function(...) {
s3_register("pillar::pillar_shaft", "vctrs_vctr")
s3_register("tibble::type_sum", "vctrs_vctr")
}Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.