Dear list,
I was wondering how to best implement some sort of a "plugin" paradigm
using R methods and the dispatcher:
Say we have a function/method ('foo') that does something useful, but
that should be open for extension in ONE specific area by OTHERS using
my package. Of course they could go ahead and write a whole new 'foo'
method including the features they'd like to see, but that's not really
necessary. Rather, they should be able to just write a new "plugin"
method for that part of 'foo' that I'd like to open for such plugins.
The way I chose below works, but generates warnings as my method has
signature arguments that don't correspond to formal classes (which is
totally fine). Of course I could go ahead and make sure that such
"dummy" classes exist, but I was wondering if there's a better way.
It'd be great if anyone could let me know how they handle "plugin"
scenarios based on some sort of method dispatch!
Thanks,
Janko
##### CODE EXAMPLE #####
setGeneric(name="foo", signature=c("src"), function(src, ...)
standardGeneric("foo"))
setGeneric(name="plugin", signature=c("src", "link", "plugin"),
function(src, link, plugin, ...) standardGeneric("plugin")
)
setMethod(f="plugin", signature=signature(src="character", link="foo",
plugin="punct"),
function(src, link, plugin, ...){
out <- gsub("[[:punct:]]", "", src)
return(out)
}
)
setMethod(f="plugin", signature=signature(src="character", link="foo",
plugin="digit"),
function(src, link, plugin, ...){
out <- gsub("[[:digit:]]", "", src)
return(out)
}
)
setMethod(f="foo", signature=signature(src="character"),
function(src, plugin=NULL, ...){
if(!is.null(plugin)){
if(!existsMethod(f="plugin",
signature=c(src=class(src), link="foo", plugin=plugin)
)){
stop("Invalid plugin")
}
.plugin <- selectMethod(
"plugin",
signature=c(src=class(src), link="foo", plugin=plugin),
useInherited=c(src=TRUE, plugin=FALSE)
)
out <- .plugin(src=src)
} else {
out <- paste("Hello world: ", src, sep="")
}
return(out)
}
)
foo(src="Teststring:-1234_56/")
foo(src="Teststring:-1234_56/", plugin="punct")
foo(src="Teststring:-1234_56/", plugin="digit")
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