Let me peel this one question about config const/var help off separately:
>> For example, given:
>>
>> config var m = 10,
>> n = m;
>>
>> would you prefer ./a.out --help to say:
>>
>> m = 10
>> n = m
>>
>> or:
>>
>> m = 10
>> n = 10
>
> The second is fine. It's mostly so the user can see what value a
> variable would have if it's not provided on the command line.
So then the follow-up question is: Does the second form here suggest to
you that if I run:
./a.out --help
and see:
m = 10
n = 10
that if you run:
./a.out --m=100
then n will still be 10? (because it won't, it'll actually be 100). This
is what made me ask about the first form.
On the other hand, the first form has the downside that if you have a
complicated initializer like:
config var n = computeProblemSize(Locales, m, pi);
then seeing the following in your help message:
n = computeProblemSize(Locales, m, pi)
isn't actually very helpful. So maybe you actually want both to avoid
both of these pitfalls. :(
The other challenge/downside to printing out the values (m=10, n=10) is
that it requires a potentially non-trivial amount of code to execute in
order to print out the help message. For example, we have benchmarks
today that do a computeProblemSize() routine like the above that queries
the memory of all the locales on which the program is running, adds them
up using a reduction, and computes the problem size based on the result.
This suggests that running ./a.out --help would require launching the job
across a number of nodes (potentially waiting in a queue before getting
the opportunity to do so if running on a shared resource) before printing
its result.
For this reason, if I had to pick just one of these two approaches, I'd
probably pick the one that prints the initializing expression since it
reduces the chances of confusion and doesn't require executing any of the
program to accomplish. If combined with user-supplied help text for each
variable, it seems like one could avoid cases where the initializing
expressions alone were too confusing.
Any other reactions?
Thanks,
-Brad
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