From: "David A. Black" <dblack@...>
Date: 2008-04-05T19:13:27+09:00
Subject: Re: The ||= assignment operator

Hi --

On Sat, 5 Apr 2008, Avdi Grimm wrote:

> On this topic, am I the only one who would really like to see a
> dedicated "defaulting operator" in Ruby?  Something that actually has
> the semantics which a lot of people mistakenly assume for ||=, i.e.
> "assign if and only if nil"?  I think Perl6 uses the //= operator for
> this.  This is such a subtle gotcha.  I've seen a lot of code that was
> potentially buggy because it didn't account for the fact that the
> 'false' value would be handled incorrectly.

The false value isn't handled incorrectly, though. The test is for
boolean falseness, and both nil and false always pass that test.  If
you need x to be a certain value (nil or any other), you should test
for exactly that value.

Also, it's not exactly that the lhs of ||= is nil. ||= will allow
uninitialized local variables, which are not nil:

irb(main):003:0> a ||= 1
=> 1
irb(main):004:0> b || b = 1
NameError: undefined local variable or method `b' for main:Object
 	from (irb):4

So we'd be getting into a thing with "uninitialized or nil, but not
false" which seems very use-case specific to me. I'd rather let the
boolean significance just do its thing.


David

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