From: Brian Candler <b.candler@...>
Date: 2010-06-16T02:24:19+09:00
Subject: Re: shorthand

Roger Pack wrote:
> I read this once:
> 
> Operator ||= can be shorthand for code like:
>  x = "(some fallback value)" unless respond_to? :x or x
> 
> How would that look like exactly, in shorthand, any guesses?

foo ||= 5

is shorthand for

foo = foo || 5

which means
(a) 'foo' is a local variable (because it's an assignment)
(b) it will be set to 5 if it is currently nil or false, otherwise it 
will retain its previous value.

The thing you read about respond_to? is wrong. This construct is nothing 
to do with a method called foo, as you can easily demonstrate:

$ irb --simple-prompt
>> def foo
>> 9
>> end
=> nil
>> respond_to? :foo
=> true
>> foo ||= 5
=> 5
>> foo
=> 5
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