From: Robert Klemme <shortcutter@...>
Date: 2009-10-31T00:05:10+09:00
Subject: Re: Ruby doesn't implement x++ for Fixnum's because ???

2009/10/30 RichardOnRails <RichardDummyMailbox58407@uscomputergurus.com>:

> I'll correct my errors and probably have a new theory subsequently.

IMHO the story goes like this: absence of postfix ++ and -- is a
consequence of the fact that numeric types are immutable in Ruby which
makes an assignment necessary for these operators.  Although that
would be doable, it would not immediately be obvious when looking at
"foo++".  On the other side, "foo += 1" makes the assignment obvious
while still being pretty concise (you do not have to write "foo = foo
+ 1").

Which brings us to the question: what is the advantage of immutable
numbers?  First, it avoids errors that could be caused by aliasing
(two objects refer the same object, one of them changes it, it changes
for the other one as well without being expected).  Then, it is quite
natural if you consider mathematical numbers: they cannot change.

Additionally, the expression "1" can always refer to the same object
(in reality it's a bit different but from a Ruby programmer's
perspective the difference is not noticeable) which in fact makes
using numeric constants very efficient (as opposed to the expression
"'foo'" which constructs a new String instance on every invocation,
albeit with a shared char array underneath which eases the pain a
bit).

This in turn makes integer math pretty efficient because if numbers
were mutable Ruby would have to create a new object for every result
of an operator evaluation.  I am not saying that Ruby is ideal for
number crunching but it could be significantly slower if certain
design decisions would have been made differently.

Kind regards

robert

-- 
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