+ # Return an error object in case of error.
+ #
+ # assert "/etc".chdir == null
+ # assert "/fail/does no/exist".chdir != null
+ # assert getcwd == "/etc" # unchanger
+ fun chdir: nullable Error
+ do
+ var res = to_cstring.file_chdir
+ if res then return null
+ var error = new IOError("Cannot change directory to `{self}`: {sys.errno.strerror}")
+ return error
+ end