Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!de-l.enfer-du-nord.net!feeder2.enfer-du-nord.net!talisker.lacave.net!lacave.net!not-for-mail From: Kevin Mahler Newsgroups: comp.lang.ruby Subject: Re: scope of assignments with lambda Date: Fri, 15 Apr 2011 01:37:17 -0500 Organization: Service de news de lacave.net Lines: 43 Message-ID: <90f821efcacb67d7fe0de170d6979e29@ruby-forum.com> References: <5ab8b94d707235d7b83c9b011b696ef4@ruby-forum.com> <2b8e0c638f80e0062cbba1f68ca297d8@ruby-forum.com> <470a9e96982d7a927f140193f12c0f64@ruby-forum.com> NNTP-Posting-Host: bristol.highgroove.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Trace: talisker.lacave.net 1302850299 54585 65.111.164.187 (15 Apr 2011 06:51:39 GMT) X-Complaints-To: abuse@lacave.net NNTP-Posting-Date: Fri, 15 Apr 2011 06:51:39 +0000 (UTC) In-Reply-To: <470a9e96982d7a927f140193f12c0f64@ruby-forum.com> X-Received-From: This message has been automatically forwarded from the ruby-talk mailing list by a gateway at comp.lang.ruby. If it is SPAM, it did not originate at comp.lang.ruby. Please report the original sender, and not us. Thanks! For more details about this gateway, please visit: http://blog.grayproductions.net/categories/the_gateway X-Mail-Count: 381610 X-Ml-Name: ruby-talk X-Rubymirror: Yes X-Ruby-Talk: <90f821efcacb67d7fe0de170d6979e29@ruby-forum.com> Xref: x330-a1.tempe.blueboxinc.net comp.lang.ruby:2920 Fearless Fool wrote in post #988777: > What I was surprised about was the scoping of variables in assignment > statements. I guess it makes sense. Assume that p is previously > undefined, then a reference on the RHS to p like this: > > p = p + 1 > > will raise an error. But wrapped inside a lambda, the reference to p is > deferred, so it all works: > > p = lambda { |n| p.call(n-1) if (n > 0) } > > As I said, that's the power of a lexical closure. "The scoping of variables in assignment" is exactly the same in both cases. p = p + 1 does not fail because p is undefined. p is defined. Its value is nil. The error results from NilClass#+ not existing. This has nothing to do with "the power of the lexical closure". Local variables are discovered at compile time. p gets defined at the beginning of the scope, *before* the line "p = p + 1", and it's assigned the value of nil. Try p = p.to_i + 1 and observe the non-error. Even better, try def foo puts local_variables #=>bar bar = 99 end The reference to p inside the lambda is not deferred. At compile-time, the p inside the lambda is bound to the local variable p, just as the p on the right-hand side of "p = p + 1" is bound to the local variable p. There is nothing special going on as a result of the lambda being present. -- Posted via http://www.ruby-forum.com/.