From: sur max <sur.max@...>
Date: 2007-03-14T17:59:06+09:00
Subject: Re: Where is my Class ?

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Hi Pit,

from your explanation and my perception too it seems that we are not able to
write anything in the constants once they defined.
Look at this then....

B=Class.new  # B

B.module_eval{define_method :foo do; puts "foo here"; end}   #
#<Proc:0x02deeb18@(irb):3>

B.instance_methods.include?("foo")   # true

B.__id__  # 24100884

a=Class.new  # <Class:0x2de7978>

a.module_eval{define_method :bar do; puts "bar here"; end}
#<Proc:0x02de2920@(irb):7>

a.__id__  # 24067260


a.instance_methods.include?("foo")   # false

a.instance_methods.include?("bar")  # true

 B=a  # warning: already initialized constant B
=> B

a.instance_methods.include?("bar")  # true

a.instance_methods.include?("foo")  # false

B.instance_methods.include?("foo")  # false

B.instance_methods.include?("bar")  # true

B.__id__  # 24067260

B.__id__==a.__id__ #  true

this means that the Class B is overwritten by the Class referenced by "a"
so it is the case of changing a constant. Is that possible ?

On 3/14/07, Pit Capitain <pit@capitain.de> wrote:
>
> sur max schrieb:
> > assignment happened LEFT-to-RIGHT
> >
> >> a = Class.new
> >> #  #<Class:0x2de1f00>
> >>
> >> B = Class.new
> >> # B
> >>
> >> B=a
> >> it gives
> >> # warning: already intialized constant B .... thats fine
> >>
> >> but
> >> and now if i check a as
> >>
> >> a
> >> # B
> >>
> >> so where is the original class of a that was #<Class:0x2de1f00> ....
> and
> >> how
> >> come the assignment happens from RIGHT-to-LEFT ?
> >>
> >> any idea ?
>
> sur max, you still have the same class, accessible via both a and B:
>
>    a = Class.new  # => #<Class:0x310b640>
>    a.object_id    # => 25713440
>
>    B = Class.new  # => B
>    B.object_id    # => 25706400
>
>    B = a          # warning: already initialized constant B
>                   # => B
>    a              # => B
>    a.object_id    # => 25713440
>    B.object_id    # => 25713440
>
> The reason is that Ruby uses the name of the first constant a class
> object is assigned to as the class' name:
>
>    X = Class.new  # => X
>    Y = X          # => X
>    Y              # => X
>
> In your case, you created an "anonymous" class without assigning it to a
> constant, so it doesn't have a name yet. After assigning this anonymous
> class to the constant B, you get the warning, but nethertheless the
> constant is changed to reference the previous anonymous class. After the
> assignment, the class isn't anonymous anymore, it has got the name "B".
>
> This way you can create multiple classes with the same name:
>
>    c1 = Class.new  # => #<Class:0x30f60c4>
>    c2 = Class.new  # => #<Class:0x30f3aa4>
>
>    C = c1          # => C
>    C = c2          # warning: already initialized constant C
>                    # => C
>
>    c1              # => C
>    c2              # => C
>
> They still are distinct classes, though.
>
>    c1.object_id    # => 25669730
>    c2.object_id    # => 25664850
>
> Regards,
> Pit
>
>


-- 
sur
"is a String object" is a String object
http://expressica.com

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