On 25.04.2016 16:38, Leon Rosenberg wrote:
On Mon, Apr 25, 2016 at 4:13 PM, Christopher Schultz <
ch...@christopherschultz.net> wrote:
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Leon,
On 4/22/16 12:24 PM, Leon Rosenberg wrote:
Hi guys,
I would always choose the case with the elses.
First, I think it's more clear: if you expect that only one branch of
the code will run, and no others, then the elses tell the reader that
fact without any further commentary. The zero-else case might help you
catch some logic errors (because for example you can log each entry
into a branch) but there are of course other ways to do that.
Second, it's more efficient, regardless of what type of processor you
have. Let's take an example where there are more than 3 branches. How
about something like a million branches (just to accentuate the
point)? If one of the branches runs, the others are skipped. If all
branches have an equal change of being chosen, then the CPU has to
perform on average 500000 predicates. If you put the common cases at
the top, you can do even better. Let's assume the 80/20 rule applies,
here, and you can take a guess that, on average, the CPU will only
have to perform 100000 predicates on average.
I don't think the example is valid (even if machines with 100.000 cpus and
more actually exist). But I remember from days of my study, which lies way
way back, that languages that are optimized for parallel processing would
be able to tell the compiler to execute all ifs in parallel. So if we stick
with a number of ifs which is less than the number of available cores/pipes
we could run it all in parallel. I don't think it is possible with if else,
unless it is transformed into something else.
The other thing that made me wonder is that most people on the list (or all
except me) actually considered if-else-if-else more readable. It not only
creates a more complex structure (visually and syntactically (more
letters)). But also the semantics of an *else* are different as of an *if*.
This is like North Carolina ;-)
if (man){ do_man_thing; } else { do_woman_thing(); } doesn't work anymore,
even it worked 20 years ago. Talking about maintaining :-)
And one more thing, as we all write programs that should last for 20 years at least, is
the advent of quantum computers. What would be the correct (maintainer-friendly) answer
once the mere action of testing for a condition may change it ?
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