CFURLRef  desktopURL = fn FileManagerURLForDirectory( NSDesktopDirectory, NSUserDomainMask )
CFURLRef         url = fn URLByAppendingPathComponent( desktopURL, @"file.txt" )
CFDictionaryRef dict = fn FileManagerAttributesOfItemAtURL( url )

print dict[@NSFileModificationDate] // Read file's current date

// Reset file date to current
fn FileManagerSetAttributesOfItemAtURL( CFURLRef url, @{NSFileModificationDate:fn DateNow )