W dniu 2014-04-27 17:01, Lee Winter pisze:
The problem I see is that the above command uses a file, a.out.icon,
for both input and output. Tup's file usage model is very primitive.
A rule is allowed to use a file for only input or for only output. I
suspect this simplifies the DAG because writing a file, reading it,
and re-writing it, as you attempted above, makes the DAG more complex.
It shouldn't be a problem, but it is.
Just use two different names for the files and the "problem" is
solved... Using the same file for input and output is not worth any
trouble, as that is an endless source of problems, while this feature
has no real value...
In case you overwrite the input file with the output such "feature"
makes no sense at all.
In case you append to the input file with additional output the problem
is that this just doesn't fit the model of building - what would you do
if the "basic" part of the source (the ones which CREATE the file) don't
change, and the "append" part does? You cannot "unappend" it before
appending the changed part, so you have to build that from scratch...
Additional problem is when you have rules which only read from such file
- do they read the version before or after the modification? Whichever
you choose its just your preference and everyone has his/her own... So
either you have to complicate the syntax to explicitly state that (what
about a case where you have 100 such read-write rules for a single
file?) or the creator of software has to decide for everyone, making the
"opposite camp" dissatisfied.
In return you get no real value, as this whole "problem" can be easily
avoided by just using different name for the output file.
Regards,
FCh
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