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From Phil Steitz <>
Subject Re: [math][dbcp][pool] Apachecon NA (Austin)
Date Sun, 04 Jan 2015 21:37:41 GMT
On 1/4/15 5:58 AM, Gilles wrote:
> Hello.
> On Sun, 04 Jan 2015 12:09:35 +0100, Luc Maisonobe wrote:
>> Hi all,
>> Le 04/01/2015 02:07, Gilles a écrit :
>>> On Fri, 02 Jan 2015 14:45:15 -0700, Phil Steitz wrote:
>>>> I am thinking about submitting a proposal or two for Austin.  I
>>>> could update / extend the pool/dbcp talk I did last year or try a
>>>> [math] talk.  I would love to have company developing and / or
>>>> presenting either of these.  Is anyone else interested in
>>>> working on
>>>> a talk on either of these?  Any suggestions on content?
>>>> For [math] I have always wanted to do a high level overview
>>>> followed
>>>> by some real world examples.  It would be great to make the
>>>> examples
>>>> part a community effort.
>>> It reminded me that I had yet to improve one toy example in the
>>> "src/userguide/java/org/apache/commons/math3/userguide" section
>>> of the repository.
>>> It also occurred to me that I don't know how to compile and run
>>> the applications stored there. :(
>>> Is there a maven incantation to do so?
>> No as maven does not know about this directory (and should not
>> IMHO).
> I think that we should have some way to
> 1. automatically compile its content (so that we can ensure that the
>    source tree does not contain any non-compilable stuff) and
> 2. run selected classes (so that users easily see CM code at work)
> It looks like it should not be too difficult (for an experienced
> maven user, which I'm not) to create a profile for doing just that.
> [I've seen there is an "exec" plugin that could do (2), but I
> couldn't find where one can specifytan alternate source for
> compilation.]
>>>> For [pool] / [dbcp] I did the boring part last year - summary of
>>>> changes in the 2.x versions, migration, etc. - so this year I
>>>> could
>>>> focus on examples and best practices.  Again, a great thing to
>>>> work
>>>> together on.
>>>> Another crazy idea I have had is a talk on how hard it is to
>>>> design
>>>> stable APIs, using [math] as an example.
>>> Is it really hard?  Isn't it rather that some developers just lack
>>> the willpower to support less than ideal APIs? :-}
>> Yes, it is hard.
> I wanted to stress exactly what you expand below, i.e. that needs are
> changing, and that if we want to combine all the qualities of good
> code (a.o. code that evolves with the developers' community, with
> the users' community, with the language's state-of-the-art, with the
> computers' power, etc.) we have to modify the APIs; it is a never
> ending, but creative, task.
> The alternative is, as I wrote above, to stick with less-than-ideal
> APIs, and _that_ is not hard; but it is a dead end.

If you make good choices initially, it does not have to be a dead
end.  That's the challenge.  Some of our APIs have been pretty
stable.  The problem with constantly changing APIs is they become
effectively worthless for real world use.  Even for me, as a *math
developer*, I have some of my own hacked / forked / semi-patched
versions of [math] things because I don't have time to refactor and
retest all of the code that uses now compat-broken stuff.   I am not
advocating that we don't ever change APIs - just that we be
conservative in doing so so that users can count on some level of
stability.  Somehow R does this pretty well.

The last comment is what I was thinking about exploring when I said
that modeling math algorithms using OO constructs is tricky.  Maybe
they are just much smarter than us (to some extent, I am sure that
is true); but I think R also has the advantage that it is really a
pretty much procedural setup (I know, R is weirdly OO in its own
way; but the public API is really pretty flat, procedural). 

The other thing that I was thinking about in this area is basically
what the whole field of numerical analysis is about - the difference
between naive modelling of mathematical objects in the "natural" way
and what you need to do to get stable and accurate results.  Also,
the tradeoff between "correctly" handling corner cases and
extensions beyond what is well-defined mathematically and
performance.  The Complex class illustrates all of these things.
>>>> That talk would also call
>>>> out some of the special challenges that you run into modelling
>>>> mathematical objects using OO constructs.
>>> That would be interesting.
>>> Are mathematical concepts really more special to model than other
>>> concepts?
>> No, the problem is that low level reusable components intended to be
>> used by lots of different users for lots of different needs are
>> difficult to set up. You have to meet conflicting needs and the
>> developers do not know in advance how their code will be used.

That is the core problem of API design, which we all three agree is
"hard."  As mentioned above, I really think that math presents some
special challenges, mostly having to do with the fact that "natural"
representations of things sometimes lead to both bad numerics and
bad extensibility.
> That's what I wrote below: "trying to implement generic algorithms
> to solve as many practical problems as possible".
> Thus: it is good to have generic, reusable, code (e.g. just from a
> maintenance POV), but it at some point, it will conflict with
> unexpected usage. Hence API change will be in order.
>> In many cases, things start with "someone scratching an itch"
>> because
>> open-source developers are the first users of their stuff. The
>> resulting
>> API is biased towards this first need. Low level reusable components
>> developers have to make lots of efforts to design something clean
>> enough to anticipate other uses. Even experienced low level reusable
>> components developers don't succeed in this part.
> I totally and did not say otherwise.
> The wrong way would be to have duplicate code all over the place to
> tak care of each new usage. Since we try to avoid that, we'll need
> to refactor when the "genericity" in one direction conflicts with
> unanticipated usage.
>>> I rather think that the issues arise from trying to sort out the
>>> general from the particular, trying to implement generic algorithms
>>> to solve as many practical problems as possible.
>> Perhaps, but it is really an important need for reusable components.
> From a development POV, I thinks so too.
> For black-box users, it is not. [They don't care about what's in the
> box as long as it does the job; and "no duplicate code" is, for
> instance, not a requirement.  But this a short-term view, since
> maintenance will suffer and loss of quality will ensue.]
>> Another problem is that not moving forward (typically still staying
>> in the 3.X series instead of starting 4.0) creates additional
>> constraints. Trying to patch something wrong is much more difficult
>> than rewriting it, and sometimes it is even completely impossible if
>> wrong design choices cannot be changed.
> +1
>>> This quite naturally lead to desing decisions that may be
>>> challenged
>>> by the appearance of unforeseen cases (or better programming
>>> skills).
>> Exactly. However, I prefer to say that here is the problem, and
>> it is
>> a challenge we have to consider rather than saying it is
>> something we
>> don't want to cope with so we ignore the problem and don't care
>> about
>> users apart from our own needs.
> So, we perfectly agree: i.e. we do not have the willpower to maintain
> old cruft! :-)
>>>> Might be a little painful
>>>> to develop, but also maybe a little cathartic ;)
>>> It would certainly be useful to understand where the pain really
>>> comes from.
>> There is an old joke I have heard numerous times in different
>> activities (including outside of software development): remove
>> the user and everything gets way better.
> Sure (including us!).
> But my question was real: we cannot make the user disappear, nor
> all the reasons why we write programs, so we have to let the APIs
> evolve.  Why is there such pain in doing so?

Basically because constant compat breaks screw users.  The win-win
is obviously to do the hard thinking, compromising and testing to
get to stable APIs that we can extend without breaking existing APIs.

> Best,
> Gilles
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