[task #15109] Arithmetic not reading data when metadata requested

[Mohammad Akhlaghi]

Update of task #15109 (project gnuastro):

                 Summary: Size of dataset as an Arithmetic operator =>
Arithmetic not reading data when metadata requested

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Follow-up Comment #17:

Great! your commit
<http://git.savannah.gnu.org/cgit/gnuastro.git/commit/?id=4068336> is now in
the Gnuastro's main `master' branch. Some further corrections were necessary,
which I implemented in the next commit
<http://git.savannah.gnu.org/cgit/gnuastro.git/commit/?id=ddcb77a760>. Please
go through those points and look at the corrected lines to hopefully prepare
you for your next edits in the code ;-).

But as you may have noticed, I just changed the task summary/title, I didn't
close it. The reason is that we still need to read-in the full dataset to just
read its size. However, as mentioned in the first comment of this task, we
don't want this: when only the dataset's metadata is necessary, we shouldn't
read the data (and waste time and memory). So to complete this task, we should
add some special steps in the arithmetic program so when meta-data are
necessary, it doesn't go reading-in the full dataset. For example a special
variable/flag called `meta' can be defined in the relevant functions. The 
`size' operator (or other later operators) will set it to 1, while the others
will set it to zero. When its 1, then the step where we pop the operator
(either read it, or just pick it from the stack), we just read/copy the
metadata in an empty-of-data dataset.

But this may be a little too low level for you Sachin and isn't a critical
issue now. So I recommend moving onto another task/bug. Thanks again for the
good work ;-).

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