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Leon,
On 4/25/16 10:38 AM, Leon Rosenberg wrote:
> On Mon, Apr 25, 2016 at 4:13 PM, Christopher Schultz <
> ch...@christopherschultz.net> wrote:
>
> 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.
While there may be some systems that do this kind of thing, Java isn't
one of them. Java is single-threaded unless you explicitly dispatch
work to other threads.
If you use else-less-if, then there is never an opportunity for
parellelization, since the program is going to assume that those
predicates are (a) independent and (b) ordered in a way that the
programmer intended.
If you use if-with-else then those statements are also in intentional
order and -- at someone else said elsewhere in this thread -- the
predicates may have side-effects that could be dangerous to execute
out-of-order (or just "early").
>> 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 :-)
You *did* mention that the cases were all mutually exclusive. This is
precisely what if/elseif was designed for.
- -chris
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