Comments on: Check for nil and initialize on a single line http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/ Because programming should be fun Tue, 06 Jan 2009 03:44:04 +0000 http://wordpress.org/?v=2.1.2 By: Arne http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-61 Arne Wed, 04 Apr 2007 14:31:29 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-61 I always forget there's a nil? message, usually I do the ||=. Just curious, what's a fleebie? I always forget there’s a nil? message, usually I do the ||=.

Just curious, what’s a fleebie?

]]> By: Frank http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-63 Frank Wed, 04 Apr 2007 17:00:28 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-63 Fleebie is nothing really. I just thought that it would be memorable. =) There was a squirrel in some weird humor show. I don't recall how they called it exactly, but it somewhat sounded like "ruby fleebie". I would have prefered to tell you another reason... Fleebie is nothing really. I just thought that it would be memorable. =)

There was a squirrel in some weird humor show. I don’t recall how they called it exactly, but it somewhat sounded like “ruby fleebie”.

I would have prefered to tell you another reason…

]]> By: zerohalo http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-65 zerohalo Wed, 04 Apr 2007 17:57:16 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-65 Something that I find odd about the nil? method is the differentiation between an object being nil and the non-existence of an object. They are not the same. Consider: >> puts x = 1 if x.nil? => 1 >> puts 'z is not defined' if z.nil? => NameError: undefined local variable or method 'z' How is that explained? In the first instance, the nil? method is obviously creating the x object, assigning nil to it, and then assigning the value 1. In the second instance, nil? is not creating the z object and thus returning an error. Something that I find odd about the nil? method is the differentiation between an object being nil and the non-existence of an object. They are not the same. Consider:

>> puts x = 1 if x.nil?
=> 1
>> puts ‘z is not defined’ if z.nil?
=> NameError: undefined local variable or method ‘z’

How is that explained? In the first instance, the nil? method is obviously creating the x object, assigning nil to it, and then assigning the value 1. In the second instance, nil? is not creating the z object and thus returning an error.

]]> By: Frank http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-66 Frank Wed, 04 Apr 2007 18:28:13 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-66 Zerohalo, that's a very good observation. Part of the answer is because "=" binds higher than the if modifier. So, in your first example, x is assigned before the condition is executed. That's why ruby doesn't complain. However, I'm not sure about the rest of the story. I GUESS that a nil object is assigned to x at this exact moment and NOT the fixnum 1. Otherwise the if modifier would always returns false... Zerohalo, that’s a very good observation.

Part of the answer is because “=” binds higher than the if modifier. So, in your first example, x is assigned before the condition is executed. That’s why ruby doesn’t complain.

However, I’m not sure about the rest of the story. I GUESS that a nil object is assigned to x at this exact moment and NOT the fixnum 1. Otherwise the if modifier would always returns false…

]]> By: zerohalo http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-68 zerohalo Wed, 04 Apr 2007 21:00:14 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-68 Frank, since I was curious, I posted the question on the Ruby mailing list, and found the answer. In brief, Ruby sees x and figures it must refer to a variable and therefore creates that variable x, assigning nil value to it, before running x.nil? In the second instance, since the first reference to z is z.nil? and therefore Ruby assumes z is a method rather than variable, does nothing, and therefore z.nil? throws and exception. See here: http://www.ruby-forum.com/topic/103808 Frank, since I was curious, I posted the question on the Ruby mailing list, and found the answer. In brief, Ruby sees x and figures it must refer to a variable and therefore creates that variable x, assigning nil value to it, before running x.nil? In the second instance, since the first reference to z is z.nil? and therefore Ruby assumes z is a method rather than variable, does nothing, and therefore z.nil? throws and exception.

See here:

http://www.ruby-forum.com/topic/103808

]]> By: Frank http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-69 Frank Wed, 04 Apr 2007 21:46:35 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-69 Very interesting... I read the post you are relating to and it's not too far away from what I was thinking. Very interesting… I read the post you are relating to and it’s not too far away from what I was thinking.

]]> By: Chris http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-75 Chris Thu, 05 Apr 2007 01:58:16 +0000 http://www.rubyfleebie.com/check-for-nil-and-initialize-on-a-single-line/#comment-75 The difference between 1) x = get_some_object if x.nil? and 2) x ||= get_some_object is that in the first instance x will get reassigned only when it's nil, while in the second it will get reassigned if it's nil or false. Something to know, just in case. The difference between

1) x = get_some_object if x.nil?

and

2) x ||= get_some_object

is that in the first instance x will get reassigned only when it’s nil, while in the second it will get reassigned if it’s nil or false.

Something to know, just in case.

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