Christian Neukirchen wrote:

> Florian Gro<florgro / gmail.com> writes:
> 
> 
>>Ruby Quiz wrote:
>>
>>
>>>	# metakoans.rb is an arduous set of exercises designed to stretch
>>>	# meta-programming muscle.  the focus is on a single method 'attribute' which
>>>	# behaves much like the built-in 'attr', but whose properties require delving
>>>	# deep into the depths of meta-ruby.
>>
>>Here we go then.
>>
>>I have a golfed (8 lines) and a regular solution (21 lines) and
>>generally do the simplest thing that makes the tests work.
>>
>>Got it to run in two tries by the way. I failed the fourtytwo test at
>>first. After that everything worked fine. :)
> 
> 
> Here's my solution, done in two tries too.  Took about 15 minutes, I
> think.
> 
> 
> class Module
>   def attribute(a, &block)
>     if a.kind_of? Hash
>       a, default = a.to_a.first
>     else
>       default = nil
>     end
> 
>     a = a.to_sym
>     ivar = "@#{a}"
> 
>     define_method(a) {
>       if instance_variables.include? ivar
>         instance_variable_get ivar
>       else
>         block ? instance_eval(&block) : default
>       end
>     }
>     define_method("#{a}=") { |v| instance_variable_set ivar, v }
>     define_method("#{a}?") { !!__send__(a) }
>   end
> end
> 

This demonstrates a problem I have with many solutions -- taking
Florians as an example.

class Test
   attribute 'a'
end

tst.a?         # => false   OK
tst.a = false  # => false   OK
tst.a?         # => false   This should be true


Regards,

Michael

-- 
Michael Ulm
R&D Team
ISIS Information Systems Austria
tel: +43 2236 27551-219, fax: +43 2236 21081
e-mail: michael.ulm / isis-papyrus.com
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