Experimental Physics and
Industrial Control System

> That is, if we know that elements NORD through NELM-1 are not valid
> data then it seems better to not return them, unless the user
> explicitly asks for it. Then again, I think it would be preferable to
> have uniform behavior. Looking forward to hearing what the best
> approach should be...

To complicate things a little, let me just say that there is a mental model (intuitive model) that both implementations  should (maybe) conform to.
caget on a waveform should return NORD elements
caput $waveformPV $value should return an error (wrong syntax) or set the waveform to a size 1 array
caget(waveformPV,count=N,fill_value=-1.234) returns N elements where the first few are from the waveform (NORD elements) and the rest is filled with fill_value. Count can be greater than NELM, if count is -1, then returns NELM elements.

*About changing behavior and upgrading software*
I occasionally read that people are afraid to change the behavior of their software because "they are going to break their accelerator". Personally, when I upgrade, I do major QA. Additionally I allow for partial/progressive deployment . In an upgrade, I expect (minor) issues and am ready to rollback the upgrade if required.
In my view, changes are perfectly acceptable if you get closer to the mental model, i.e. make you software more intuitive and programmer-friendly. What may not be acceptable is when core developers of "collaborative" software stops their improvements because they are told that the intended changes would break their accelerator. As a result, the entire collaboration is held hostage.
Obviously it helps if the changes are documented in the release file.

Hope that helps!
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