From: "David A. Black" <dblack@...>
Date: 2005-02-13T06:45:38+09:00
Subject: Re: const_defined? and inheritance

Hi --

On Sun, 13 Feb 2005, Kevin Howe wrote:

>>>  class A
>>>    FOO = 'BAR'
>>>  end
>>>
>>>  class B < A; end
>>>
>>>  puts A.const_get(:FOO) # => 'BAR'
>>>  puts A.const_defined?(:FOO) # => true
>>>  puts B.const_get(:FOO) # => 'BAR'
>>>  puts B.const_defined?(:FOO) # => false
>>>
>
>> I think they're just two different operations.  The constants a module
>> can see ("get") is a superset of the constants it's defined.
>
> If that were the case then B.const_get(:FOO) would raise an error since B
> does not define FOO. Instead it inherits it from A, and returns the
> inherited value of "BAR". But you are probably right in the sense that
> const_defined? shows only those explicitly set in that particular class.

Yes, that's what I meant (and thought I'd said :-)  B can see A's FOO,
but B has not defined a FOO.  "defined?", on that construction, means
"defined_by_the_receiver?", rather than
"defined_somewhere_and_visible_to_the_receiver?"

> I'll just use constants.include?('FOO') instead.

To put a positive spin on it: note that Ruby gives you a way of
looking up constants on pretty much any of the possible criteria you'd
want to.


David

-- 
David A. Black
dblack@wobblini.net