From: Robert Klemme <shortcutter@...>
Date: 2008-05-02T23:20:07+09:00
Subject: Re: | versus || Any reason for this issue?

On 02.05.2008 16:01, Iņaki Baz Castillo wrote:
> Hi, why in the second case the non declared "my_var" variable is
> processed but not in the first case?

Because || does short circuit while | does not.

> irb> nil || 2 || my_var
> => 2
> 
> irb> nil | 2 | my_var
> NameError: undefined local variable or method `my_var'
> 
> Of course, I prefer the first case: 2 is already true so there is no
> reason to read the next "my_var". Also, it's not good for performance,
> is it?

"||" is the short circuit boolean "or" operator.  You cannot override 
it.  "|" on the other hand is an operator that can be overloaded and it 
does not short circuit.  It would not make any sense to make "|" short 
circuit because it can contain arbitrary functionality.

Here are some classes that implement "|":

$ ruby -e 'ObjectSpace.each_object(Module) {|cl| p cl if 
cl.instance_methods.include? "|"}'
Array
Bignum
Fixnum
FalseClass
TrueClass
NilClass

Kind regards

	robert