I'm looking for a way to use a private Apple API from within Swift code (namely, _CFPreferencesCopyApplicationMap, which allows you to look up the paths used for user defaults for any given application).
See this answer for the motivation & the Objective-C solution. I was able to do this in Objective-C with the line:
extern CFDictionaryRef _CFPreferencesCopyApplicationMap(CFStringRef userName, CFStringRef hostName);
I haven't been able to figure out how to do the same in Swift. I know it's possible to dynamically access ObjC objects at runtime using NSClassFromString or NSSelectorFromString, but as far as I can tell these can't be used with global C functions. NSInvocation likewise seems out.
It turns out that this is possible using @_silgen_name:
@_silgen_name("_CFPreferencesCopyApplicationMap")
func _CFPreferencesCopyApplicationMap(_: CFString!, _: CFString!) -> CFDictionary!
// Then, call as:
let applicationMap = _CFPreferencesCopyApplicationMap(kCFPreferencesCurrentUser, kCFPreferencesAnyHost) as? [String: [URL]]