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Subject: Re: [boost] [outcome] non-interface-related concerns
From: Robert Ramey (ramey_at_[hidden])
Date: 2017-06-03 22:39:12

On 6/3/17 2:59 PM, Gottlob Frege via Boost wrote:

> How many non-outcome things would I need to understand? Should it be
> that hard? Shouldn't outcome be easy? And how important should this be
> in a review?
> I would appreciate answers to that from not just Niall, but anyone
> else who understands the inner workings (as it is always hard for the
> author to see their work from someone else's perspective).

> P.S. the internals of many (most?) boost libraries are hard to
> understand - too many macros, etc. Is Outcome on the same level,
> better? worse? Even if it is on the same level of most of boost, I'm
> sad :-(

I'm going to rephrase this question in a more general form.

Is it important to understand the internal implementation of a library?
If the answer is yes, how important is it?

To me the central questions are:

a) is this library intuitive to use correctly?
b) is this library hard to use incorrectly?
c) is it more work to figure out the above than it is to just write the
functionality from scratch? That is, is usage of the library economic?

d) can I verify that it actually does what I think it does?

a, b, c are basically variations on the same idea. I need yes answers to
all of these. Get to "yes" on these will involve reviewing
documentation, and sometimes tests, examples and code which implements
the library. In addition to these things, the library will need a
clearly stated purpose describing what it is meant to do. "parse any
json file so contents can be easily processed by a user's program" is
such a statement. In other words can I understand what this thing does
without having fill my head with a lot of detail. If I can't do this I
can't use it. I know this sounds trivial - but it's not. It's amazing
how many boost libraries don't pass this bar - and boost is way better
than most.

Assuming we're past a, b, and c - what about d)? Why do I need to care
about what's under the covers. There are a couple of reasons.

a) I want to be able to verify that it in fact works the way I think it
does. I want to see what the code does. No, I'm not necessarily going
to go through it line by line, but I expect to be able to trace down to
the bottom for a few cases to know that it is in fact doable should I
need to track down some problem. But more than that, if I can't do this
even for a couple of cases, I don't have confidence that the
implementation is reliable. Testing is helpful in convincing me there
is quality there. But it's not the same as knowing I trace through some
cases and verify that it does every required step and only those
required steps. Only then can I feel confident in using the code in
something important.

I realize that this is a very, very high bar that most of us boost
authors have difficulty meeting. It's just very hard. It takes a lot
of work, stamina and brain power. More tools, tests, etc can't do all
the work. It's just very hard.

So, I'm inclined to stick to things that are simpler to understand.
(usually). Something like shared_ptr I and understand. something like
state_saver I can understand. I could probably understand outcome but
I'm concerned that something which would seem so simple can require this
amount of discussion. It's just not easy to be confident about it under
these circumstances. Note that it's quite possible that were it
presented in a different manner, I might have a totally different
opinion. I'm not saying it's bad, I'm saying I can't understand it in
the time I think it would take to write my own less general version.

But I also have to mention things like spirit, serialization,
boost.units. These are things that one can't hope to really understand
the way one really should. This might be why places like Google exclude
these types of components from their list of libraries approved for
usage at Google. But I still use them. Doesn't this contradict what I
said above? Hmmmm - yeah except the economic argument. These packages
save so much future time, I'm willing to break the other rules to
include them. There is no way I'm going write my own alternatives so
it's either use them (and pray they actually work) or just not do what
they do.

Maybe the way to say this - to quote our spiritual guide - keep simple
things simple. to which I would add - If you can.

Robert Ramey

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