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register_s3_method <- function(pkg, generic, class, fun = NULL) {
stopifnot(is.character(pkg), length(pkg) == 1)
stopifnot(is.character(generic), length(generic) == 1)
stopifnot(is.character(class), length(class) == 1)
if (is.null(fun)) {
fun <- get(paste0(generic, ".", class), envir = parent.frame())
} else {
stopifnot(is.function(fun))
}
if (pkg %in% loadedNamespaces()) {
registerS3method(generic, class, fun, envir = asNamespace(pkg))
}
# Always register hook in case package is later unloaded & reloaded
setHook(
packageEvent(pkg, "onLoad"),
function(...) {
registerS3method(generic, class, fun, envir = asNamespace(pkg))
}
)
}
.onLoad <- function(...) {
# webshot provides methods for knitr::knit_print, but knitr isn't a Depends
# or Imports of htmltools, only an Enhances. This code snippet manually
# registers our method(s) with S3 once both webshot and knitr are loaded.
register_s3_method("knitr", "knit_print", "webshot")
}
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