From: dblack@...
Date: 2006-10-02T06:29:17+09:00
Subject: Re: Fixed: dynamic include

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Hi --

On Mon, 2 Oct 2006, Florian A=DFmann wrote:

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> Hash: SHA1
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>
> Am 01.10.2006 um 21:14 schrieb David Vallner:
>
>> Florian A=DFmann wrote:
>>> To be complete here if the Exception:
>>>=20
>>> NameError: undefined local variable or method `role' for
>>> #<Class:#<Person:0x2869aa0>>
>>>=20
>>=20
>> I smell a Ruby bug / gotcha.
>>=20
>> Apparently, in metaclass scope, the surrounding scope just isn't visible=
=2E
>>=20
>> Try a workaround:
>>=20
>> person.roles.each do |role|
>>    if role.class.const_defined?('Functions')
>>        class << person
>> =09    self
>>        end.class_eval do
>>            include role.class.const_get('Functions')
>>        end
>>    end
>> end unless person.nil?
>>=20
>> David Vallner
>>=20
>> PS: Statement modifiers after whole blocks? Ick.
>>=20
>
> Ok, I just tested it, but now even a person with a CustomerRole and no=20
> ManagerRole role has the methods once they are included, thanks anyway. :=
D
> dblack, extend works excactly the way I want it to, thank you too :)

The two techniques should give you the same results.  If you have a
case where they don't, I'd be interested in seeing it.

> Result...
>
> if person =3D self.send( dyn_finder, *find_args )
>   m_name =3D 'Functions'
>   functions =3D person.roles.inject([]) do |f,r|
>       r.class.const_defined?(m_name) and
>       f << r.class.const_get(m_name)
>   end and person.extend *functions
> end

That call to inject will always return an array, so the "and" will
always flip to the right and execute person.extend *functions -- even
if functions is empty, in which case you'll get an error.  You'd
probably want to drop the "and" and just do a conditional test:

   person.extend *functions unless functions.empty?


David

--=20
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org
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