From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-01-19T00:31:50+09:00
Subject: Re: What does ||= represent in this situation?

On Mon, Jan 18, 2010 at 2:27 PM, John Merlino <stoicism1@aol.com> wrote:
> anler hp wrote:
>> hello, the operator | | = is the same as the typical + =, -= and so
>> on, why did exist in ruby and not in other languages is because in
>> ruby any expression returns a value.
>> here is an example very closed but pretty much less effective in other
>> language
>>
>> a = false;
>> a || a = c;
>>
>> this means, makes a = c only if a is false�, same things happen with
>>
>> a ||= c  -- equivalent to --> a = a || c (if a is false, the right
>> side of the || will be evaluated and its value will be returned -this
>> only happen in ruby-, so c is returned either true or false)
>>
>> sorry for my english
>
> So if a is true, it is returned. If a is false, c is returned. What if a
> is undefined?


irb(main):002:0> defined? a
=> nil
irb(main):003:0> a ||= "hello"
=> "hello"
irb(main):004:0> a
=> "hello"
irb(main):005:0> defined? a
=> "local-variable"

Think of it as an idiom to set a variable to a value only the first
time. The only caveat is to take care when false is a valid value for
such variable.

Jesus.