Clarity vs. code reuse/generality

[Tim Rowe]

So is design-by-contract just another way of saying "let's hope the data
is valid, because if it's not, we're screwed"?

Not at all. Design By Contract is about assigning responsibility for
checking. If you don't assign responsibility then a pile of things end
up getting checked over and over again, because everybody is assuming
responsibility, and some things don't get checked at all because
everyone assumes that somebody else is checking.

In DbC, the pre-condition on data coming in to a program from outside
will usually simply be "true" -- nothing at all is assumed about it.
But when you pass it from an input conditioning routine to a
processing routine, the input conditioning routine should be able to
make guarantees about what it passes, and the processing routine
should be able to assume that those guarantees are met without having
to check it again (after all, what was the conditioning routine there
for?). Assertions might be useful in testing (because they save having
to repeat the same set of test cases on absolutely every test run) and
they're certainly useful in documenting, but if they're any use at all
in the production run-time then there's something wrong with your
development and testing processes.

 

[Albert van der Horst]

I'm will be teaching a programming class to novices, and I've run
into a clear conflict between two of the principles I'd like to
teach: code clarity vs. code reuse. I'd love your opinion about
it.

This seemed straightforward enough, until I realized that, to be
useful to my students in their homework, this _binary_search function
had to handle the case in which the passed function was monotonically
decreasing in the specified interval...

Here's the rub: the code above is more general (hence more reusable)
by virtue of this trick with the sense parameter, but it is also
a bit harder to understand.

This not an unusual situation. I find that the processing of
abstracting out common logic often results in code that is harder
to read, at least for the uninitiated...

Yes, of course. You're teaching, say, green belt programmers.
Good reusable code requires a fifth dan. You may not be up to it
yourself (no offense intended), let alone your students.

Writing a reusable binary search is a very different assignment
from being able to code/use it in a concrete example.

Their choice must be between *writing* a one-off binary search,
versus *using* a brilliantly code, brilliantly documented
binary search that has been given beforehand.

Even assuming the reusable code is perfect in all sense, reusing may
be more effort than writing from scratch.
Then *you* have to explain them about the benefits of reuse.
(The other benefits, of course.)

I'd love to know your opinions on this.

You're welcome.

kj

Groetjes Albert

 

[Albert van der Horst]

Which, I believe, is the only usage I've encountered of it... In
regards to quantum spin states in such things as Scientific American
(though that magazine has either gone down hill in the last 30 years, or
my expectations have gone up... Current issues read like the first years
of Discover magazine)

I dropped my subscription when power was expressed in multiples
of US hair dryers. (I could calculate that back, and was appalled
by the energy wastage of US hair dryers. ;-) )

Groetjes Albert

 

[Albert van der Horst]

Me neither.


A meaning of a word is meaningless if nobody apart the writer
understands it. The purpose of code is 1) to communicate with the

Exactly. And the OP teaches to scientist. They know sense in that
meaning. Maybe you don't, but that is irrelevant.

<SNIP>

Groetjes Albert.