From: Brian Candler <b.candler@...>
Date: 2010-02-21T23:33:28+09:00
Subject: Re: Ruby conditionals subtlety?

Eric Christopherson wrote:
> I think I understand the gist of this -- if the parser has seen foo
> already, it is considered "defined" -- but how does the distinction of
> method vs. local variable matter in this context? As far as I can
> tell, defined? works the same on local variable names and method
> names.

irb(main):001:0> bar = 123
=> 123
irb(main):002:0> defined?(bar)
=> "local-variable"
irb(main):003:0> defined?(puts)
=> "method"
irb(main):004:0> defined?(baz)
=> nil

furthermore:

irb(main):005:0> puts = "Hello"
=> "Hello"
irb(main):006:0> defined?(puts)
=> "local-variable"

So, defined?(xxx) will return non-nil if xxx is a local variable (a 
decision made at parse time), and if not then if the current object has 
a method called :xxx (which is only known at run time). Hence

foo = 123
bar if defined?(foo)

is the same as

foo = 123
bar if "local-variable"

because foo is known at parse-time to be a local variable.

Regards,

Brian.
-- 
Posted via http://www.ruby-forum.com/.