From: Mike Stok <mike@...>
Date: 2011-09-29T02:27:02+09:00
Subject: Re: Ruby Syntax @keywords ||=


On 2011-09-28, at 1:20 PM, Bhavesh Sharma wrote:

> Chad Perrin wrote in post #1024125:
>> On Thu, Sep 29, 2011 at 02:07:35AM +0900, Bhavesh Sharma wrote:
>>> Sorry if this comes across as a dumb question, but what does the
>>> following syntax mean in ruby.
>>> 
>>> @keywords ||= []
>>> 
>>> I understand that its setting the instance variable as an array but what
>>> is the logical operator '||' doing in there.
>> 
>> The ||= operator is exactly what it looks like: "or equals".  That is,
>> because every valid chunk of code in Ruby is an expression, you can read
>> "@keywords ||= []" as "give me the keywords variables value, or set it
>> equal to an empty array (and give me that)".
>> 
>> Thus, if the contents of @keywords evaluate to "true" (that is, it
>> contains some value other than false or nil), that expression simply
>> evaluates to the value of @keywords.  Otherwise, the expression assigns
>> the empty array to @keywords, and evaluates to an empty array.
> 
> Thanks Chad,
> 
> I didnt see this specific operator on
> http://www.tutorialspoint.com/ruby/ruby_operators.htm
> 
> does this mean that I can create permutations of some operators and it 
> would still be valid.

Near the top of this page is the paragraph:

For each operator (+ - * / % ** & | ^ << >> && ||), there is a corresponding form of abbreviated assignment operator (+= -= etc.)

Once you know what it means it is obvious, but it might not be obvious to a newcomer.  They are enumerated in the table at the bottom of the page.

Mike

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Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.