{"id":12917,"date":"2021-01-26T22:19:38","date_gmt":"2021-01-27T03:19:38","guid":{"rendered":"https:\/\/rud.is\/b\/?p=12917"},"modified":"2021-01-26T22:19:38","modified_gmt":"2021-01-27T03:19:38","slug":"making-it-easier-to-experiment-with-compiled-swift-code-in-r","status":"publish","type":"post","link":"https:\/\/rud.is\/b\/2021\/01\/26\/making-it-easier-to-experiment-with-compiled-swift-code-in-r\/","title":{"rendered":"Making It Easier To Experiment With Compiled Swift Code In R"},"content":{"rendered":"

The past<\/a> two<\/a> posts have (lightly) introduced how to use compiled Swift code in R, but they’ve involved a bunch of “scary” command line machinations and incantations.<\/p>\n

One feature of {Rcpp} I’ve always ? is the cppFunction()<\/code> (“r-lib” zealots have a similar cpp11::cpp_function()<\/code>) which lets one experiment with C[++] code in R with as little friction as possible. To make it easier to start experimenting with Swift, I’ve built an extremely fragile<\/em> swift_function()<\/code> in {swiftr}<\/a> that intends to replicate this functionality. Explaining it will be easier with an example.<\/p>\n

Reading Property Lists in R With Swift<\/h3>\n

macOS relies heavily<\/em> on property lists<\/a> for many, many things. These can be plain text (XML) or binary files and there are command-line tools and Python libraries (usable via {reticulate}) that can read them along with the good ‘ol XML::readKeyValueDB()<\/code>. We’re going to create a Swift function to read property lists and return JSON which we can use back in R via {jsonlite}.<\/p>\n

This time around there’s no need to create extra files, just install {swiftr} and your favorite R IDE and enter the following (expository is after the code):<\/p>\n

library(swiftr)\n\nswift_function(\n  code = '\n\nfunc ignored() {\n  print(\"\"\"\nthis will be ignored by swift_function() but you could use private\nfunctions as helpers for the main public Swift function which will be \nmade available to R.\n\"\"\")\n}  \n\n@_cdecl (\"read_plist\")\npublic func read_plist(path: SEXP) -> SEXP {\n\n  var out: SEXP = R_NilValue\n\n  do {\n    \/\/ read in the raw plist\n    let plistRaw = try Data(contentsOf: URL(fileURLWithPath: String(cString: R_CHAR(STRING_ELT(path, 0)))))\n\n    \/\/ convert it to a PropertyList  \n    let plist = try PropertyListSerialization.propertyList(from: plistRaw, options: [], format: nil) as! [String:Any]\n\n    \/\/ serialize it to JSON\n    let jsonData = try JSONSerialization.data(withJSONObject: plist , options: .prettyPrinted)\n\n    \/\/ setup the JSON string return\n    String(data: jsonData, encoding: .utf8)?.withCString { \n      cstr in out = Rf_mkString(cstr) \n    }\n\n  } catch {\n    debugPrint(\"\\\\(error)\")\n  }\n\n  return(out)\n\n}\n')\n<\/code><\/pre>\n
This new swift_function()<\/code> function \u2014 for the moment (the API is absolutely going to change) \u2014 is defined as:<\/p>\n
swift_function(\n  code,\n  env = globalenv(),\n  imports = c(\"Foundation\"),\n  cache_dir = tempdir()\n)\n<\/code><\/pre>\n
where:<\/p>\n