| This selector selects files against a mapped set of target files, selecting
all those files which are different.
Files with different lengths are deemed different
automatically
Files with identical timestamps are viewed as matching by
default, unless you specify otherwise.
Contents are compared if the lengths are the same
and the timestamps are ignored or the same,
except if you decide to ignore contents to gain speed.
This is a useful selector to work with programs and tasks that don't handle
dependency checking properly; Even if a predecessor task always creates its
output files, followup tasks can be driven off copies made with a different
selector, so their dependencies are driven on the absolute state of the
files, not a timestamp.
Clearly, however, bulk file comparisons is inefficient; anything that can
use timestamps is to be preferred. If this selector must be used, use it
over as few files as possible, perhaps following it with an <uptodate;>
to keep the descendent routines conditional. |
