From: Ara.T.Howard@...
Date: 2005-05-05T03:54:56+09:00
Subject: Re: [RCR] Object#inside_metaclass?

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On Thu, 5 May 2005, [ISO-8859-1] Florian Gro=DF wrote:

> Ara.T.Howard wrote:
>
>> this is very useful for meta-programming:
>>
>>   jib:~/eg/ruby > cat a.rb
>>   class Object
>>     def inside_metaclass?
>
> Why? Any real world samples?


   class C
     class << self
       trait 'a' =3D> 'default_value'
     end

     trait 'a' =3D> 'default_value'
   end

the first case is defining a trait (attr) with a default value at the class
scope.  obviously the default value can be set immediately.  in the second
case we are defining an instance method with a default value.  this value
obviously cannot be set now so, instead, the code generated does a lazy loo=
kup
of the default value when the value is read the first time.  the defaults a=
re
stored in the class as a class instance variable.  it's sort hard to show i=
n a
little code but __logically__ we end up with something like (greatly simpli=
fied)

   class C

     @trait_defaults =3D {
       'class' =3D> { 'a' =3D> 'default_value' },
       'instance' =3D> { 'a' =3D> 'default_value' },
     }

     def C::a
       @a =3D @trait_defaults['class']['a'] unless defined? @a
       @a
     end

     def a
       @a =3D @trait_defaults['instance']['a'] unless defined? @a
       @a
     end
   end

so i need to know, at the point of definition if we're inside a metaclass t=
o
generate the code slightly differently.  all the above is for explanation o=
nly
and is nothing like real code.

cheers.

-a
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| email :: ara [dot] t [dot] howard [at] noaa [dot] gov
| phone :: 303.497.6469
| renunciation is not getting rid of the things of this world, but acceptin=
g
| that they pass away. --aitken roshi
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