I want to write a module which, when included in another module,
destroys every method of a class in that module. I realize this isn't
really a very useful thing to do, but I want to do it to see if it can
be done. I want to actually include the module and have it replace all
existing methods of this class with just one method.
In Python you can change an object's class in the middle of your
program by reassigning its magical __class__ variable. That would be a
very simple way to implement this idea. Doesn't seem possible here,
though.
Here's an attempt which failed:
class Muppet
def show
"it's the muppet show!"
end
end
=> nil
kermit = Muppet.new
=> #<Muppet:0x123129c>
kermit.show
=> "it's the muppet show!"
class Muppet
remove_method(:show)
end
=> Muppet
kermit.show
NoMethodError: undefined method `show' for #<Muppet:0x123129c>
from (irb):36
So far so good, but I want to get rid of *every* method. Doing what I
just did programmatically, iterating over all available methods,
that's the thing which still eludes me.
None of these attempts work:
kermit.methods.each{|m| class << Muppet ; (remove_method(m)) ; end}
NameError: undefined local variable or method `m' for #<Class:Muppet>
from (irb):43
from (irb):43:in `each'
from (irb):43
kermit.methods.each{|m| class Muppet; remove_method(m.to_sym) ; end}
NameError: undefined local variable or method `m' for Muppet:Class
from (irb):44
from (irb):44:in `each'
from (irb):44
Note 1. kermit.methods will return all methods inherited or not.
Note 2. remove method is a class method, so it's evaluated in the
context of the class object, hence Muppet.instance_eval
Note 3: you could alternatively pass symbols for the method names
On 6/14/07, Giles Bowkett <gilesb@gmail.com> wrote:
I want to write a module which, when included in another module,
destroys every method of a class in that module. I realize this isn't
really a very useful thing to do, but I want to do it to see if it can
be done. I want to actually include the module and have it replace all
existing methods of this class with just one method.
In Python you can change an object's class in the middle of your
program by reassigning its magical __class__ variable. That would be a
very simple way to implement this idea. Doesn't seem possible here,
though.
Here's an attempt which failed:
>> class Muppet
>> def show
>> "it's the muppet show!"
>> end
>> end
=> nil
>> kermit = Muppet.new
=> #<Muppet:0x123129c>
>> kermit.show
=> "it's the muppet show!"
>> class Muppet
>> remove_method(:show)
>> end
=> Muppet
>> kermit.show
NoMethodError: undefined method `show' for #<Muppet:0x123129c>
from (irb):36
from :0
So far so good, but I want to get rid of *every* method. Doing what I
just did programmatically, iterating over all available methods,
that's the thing which still eludes me.
None of these attempts work:
>> kermit.methods.each{|m| class << Muppet ; (remove_method(m)) ; end}
NameError: undefined local variable or method `m' for #<Class:Muppet>
from (irb):43
from (irb):43:in `each'
from (irb):43
from :0
>> kermit.methods.each{|m| class Muppet; remove_method(m.to_sym) ; end}
NameError: undefined local variable or method `m' for Muppet:Class
from (irb):44
from (irb):44:in `each'
from (irb):44
from :0
>> kermit.methods.each{|m| Muppet.class_eval(remove_method(m))}
NoMethodError: undefined method `remove_method' for #<Object:0x349f4>
from (irb):45
from (irb):45:in `each'
from (irb):45
from :0
I have to admit, it's not necessarily a bad thing if this task proves
impossible, but I feel like it *should* be possible.
Note 1. kermit.methods will return all methods inherited or not.
Note 2. remove method is a class method, so it's evaluated in the
context of the class object, hence Muppet.instance_eval
Note 3: you could alternatively pass symbols for the method names
Note 1. kermit.methods will return all methods inherited or not.
Note 2. remove method is a class method, so it's evaluated in the
context of the class object, hence Muppet.instance_eval
Note 3: you could alternatively pass symbols for the method names
On 6/14/07, Giles Bowkett <gilesb@gmail.com> wrote:
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method #{m.inspect}")}
>
> Note 1. kermit.methods will return all methods inherited or not.
> Note 2. remove method is a class method, so it's evaluated in the
> context of the class object, hence Muppet.instance_eval
> Note 3: you could alternatively pass symbols for the method names
>
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method :#{m}")}
Muahahaha! That was awesome! Soon the world will quake in fear when I
put this information to use!
But why doesn't this work?
>> kermit.methods(false).each do |m|
?> Object.instance_eval("remove_method :#{m}")
>> end
=>
>> kermit.methods
=> 53
I tried it with Kernel also and no dice.
Tried it with something else, though, and got a great error message:
(eval):1: warning: removing `initialize' may cause serious problem
On 6/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
Hi --
On Fri, 15 Jun 2007, Rick DeNatale wrote:
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method #{m.inspect}")}
>
> Note 1. kermit.methods will return all methods inherited or not.
> Note 2. remove method is a class method, so it's evaluated in the
> context of the class object, hence Muppet.instance_eval
> Note 3: you could alternatively pass symbols for the method names
>
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method :#{m}")}
You can also just use the block form of instance_eval:
Muppet.instance_eval { remove_method(m) }
--
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw
Note 1. kermit.methods will return all methods inherited or not.
Note 2. remove method is a class method, so it's evaluated in the
context of the class object, hence Muppet.instance_eval
Note 3: you could alternatively pass symbols for the method names
On 6/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
Hi --
On Fri, 15 Jun 2007, Rick DeNatale wrote:
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method #{m.inspect}")}
>
> Note 1. kermit.methods will return all methods inherited or not.
> Note 2. remove method is a class method, so it's evaluated in the
> context of the class object, hence Muppet.instance_eval
> Note 3: you could alternatively pass symbols for the method names
>
> kermit.class.instance_methods(false).each{|m|
> Muppet.instance_eval("remove_method :#{m}")}
You can also just use the block form of instance_eval:
Code injection attack to own a RoR site possibly? That would be my guess.
- Nathan
···
On 6/14/07, Stephen Smith <4fires@gmail.com> wrote:
Why should this inspire fear?
On 6/14/07, Giles Bowkett <gilesb@gmail.com> wrote:
>
> > kermit.class.instance_methods(false).each{|m|
> > Muppet.instance_eval("remove_method #{m.inspect}")}
> >
> > Note 1. kermit.methods will return all methods inherited or not.
> > Note 2. remove method is a class method, so it's evaluated in the
> > context of the class object, hence Muppet.instance_eval
> > Note 3: you could alternatively pass symbols for the method names
> >
> > kermit.class.instance_methods(false).each{|m|
> > Muppet.instance_eval("remove_method :#{m}")}
>
> Muahahaha! That was awesome! Soon the world will quake in fear when I
> put this information to use!
>
> But why doesn't this work?
>
> >> kermit.methods(false).each do |m|
> ?> Object.instance_eval("remove_method :#{m}")
> >> end
> =>
> >> kermit.methods
> => 53
>
> I tried it with Kernel also and no dice.
>
> Tried it with something else, though, and got a great error message:
>
> (eval):1: warning: removing `initialize' may cause serious problem
>
> Muahahaha!
>
> --
> Giles Bowkett
>
> Blog: http://gilesbowkett.blogspot.com
> Portfolio: http://www.gilesgoatboy.org
>
Ah I see :(, Probably 50% of my errors come from spurious ":" ARRRRG
Muppet.send :remove_method, m ### TESTED
Sorry.
Robert
···
On 6/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
Hi --
On Fri, 15 Jun 2007, Robert Dober wrote:
> On 6/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
>> Hi --
>>
>> On Fri, 15 Jun 2007, Rick DeNatale wrote:
>>
>> > kermit.class.instance_methods(false).each{|m|
>> > Muppet.instance_eval("remove_method #{m.inspect}")}
>> >
>> > Note 1. kermit.methods will return all methods inherited or not.
>> > Note 2. remove method is a class method, so it's evaluated in the
>> > context of the class object, hence Muppet.instance_eval
>> > Note 3: you could alternatively pass symbols for the method names
>> >
>> > kermit.class.instance_methods(false).each{|m|
>> > Muppet.instance_eval("remove_method :#{m}")}
>>
>> You can also just use the block form of instance_eval:
>>
>> Muppet.instance_eval { remove_method(m) }
>
> or Muppet.send :remove_method, :m
If you have a method called "m"
--
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw
Code injection attack to own a RoR site possibly? That would be my guess.
Sort of. I'm trying to use it to build a Rails plugin called
acts_as_fox, which overrides every method on a model to return "chunky
bacon!" (It's not really that terrifying, I just kind of had a Dr.
Frankenstein moment, drunk on power type thing.)
Unfortunately, applying Rick's code directly to an ActiveRecord model
doesn't quite accomplish this, because it's missing the superclass
methods, but applying it to ActiveRecord::Base doesn't work either. I
did get it to work by doing it twice, both on the actual model and on
ActiveRecord::Base itself, but that's very unsatisfying, because I
solved the problem by cutting and pasting. (I think I understand why
it worked; ActiveRecord::Base attaches a lot of methods to its
subclasses, instead of having them inherited directly.) It also fails
to really accomplish what I want to do, because it means that making
one model acts_as_fox destroys all the other models. (I also need to
attach a method_missing to return "chunky bacon!" but that part's
obviously trivial.)
Really the quickest way to accomplish this would be to simply pop the
model out of its inheritance hierarchy - redefine the model not to
have any superclass except Object - but I don't know if that's
possible. Trying it in the most obvious way (class Foo < Object; end,
where Foo was already defined Foo < ActiveRecord::Base) results in a
TypeError with the message "superclass mismatch."
But there must be a clean way to open up the class, grab all its
methods, including those derived from superclasses, and simply
reassign them. Something like
Code injection attack to own a RoR site possibly? That would be my guess.
Sort of. I'm trying to use it to build a Rails plugin called
acts_as_fox, which overrides every method on a model to return "chunky
bacon!" (It's not really that terrifying, I just kind of had a Dr.
Frankenstein moment, drunk on power type thing.)
Unfortunately, applying Rick's code directly to an ActiveRecord model
doesn't quite accomplish this, because it's missing the superclass
methods, but applying it to ActiveRecord::Base doesn't work either. I
did get it to work by doing it twice, both on the actual model and on
ActiveRecord::Base itself, but that's very unsatisfying, because I
solved the problem by cutting and pasting. (I think I understand why
it worked; ActiveRecord::Base attaches a lot of methods to its
subclasses, instead of having them inherited directly.) It also fails
to really accomplish what I want to do, because it means that making
one model acts_as_fox destroys all the other models. (I also need to
attach a method_missing to return "chunky bacon!" but that part's
obviously trivial.)
Really the quickest way to accomplish this would be to simply pop the
model out of its inheritance hierarchy - redefine the model not to
have any superclass except Object - but I don't know if that's
possible. Trying it in the most obvious way (class Foo < Object; end,
where Foo was already defined Foo < ActiveRecord::Base) results in a
TypeError with the message "superclass mismatch."
I do sometimes wonder what would happen if the ancestry array were
writeable. It could be interesting. I haven't thought through the
possible pitfalls.
But there must be a clean way to open up the class, grab all its
methods, including those derived from superclasses, and simply
reassign them. Something like
I do sometimes wonder what would happen if the ancestry array were
writeable. It could be interesting. I haven't thought through the
possible pitfalls.
You mean, like Object#become?
Seriously, how would that play with the core classes, which don't keep their state in instance variables?
Actually the ancestry array only exists as the return value of the
ancestry method, internally it's a chain of class objects, and module
wrapper's. Some things, like including a module will alter that
chain, although there are restrictions which lead to things like the
double module inclusion problem.
Perhaps evil.rb lets you monkey with the chain, it would seem to be
within its mission.
···
On 6/16/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
I do sometimes wonder what would happen if the ancestry array were
writeable. It could be interesting. I haven't thought through the
possible pitfalls.
I do sometimes wonder what would happen if the ancestry array were
writeable. It could be interesting. I haven't thought through the
possible pitfalls.
You mean, like Object#become?
Not exactly. As I understand it, #become involves references changing
from one object to another. I'm thinking of something more like:
module M
end
a = Object.new
class << a
ancestors.unshift(M) # essentially same as a.extend(M)
end
Seriously, how would that play with the core classes, which don't keep their state in instance variables?
I'm not sure how that would matter specifically. What problem are you
envisioning? (Not that the whole thing wouldn't be a train-wreck
anyway
On 6/16/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
I do sometimes wonder what would happen if the ancestry array were
writeable. It could be interesting. I haven't thought through the
possible pitfalls.
Actually the ancestry array only exists as the return value of the
ancestry method, internally it's a chain of class objects, and module
wrapper's.
By making it writeable I meant making it an interface to the chain
itself. Obviously you can do:
Would you want to be able to switch ordering too? I wonder what kind
of interesting evil could come of that...
···
On 6/16/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
Hi --
On Sun, 17 Jun 2007, Devin Mullins wrote:
> dblack@wobblini.net wrote:
>> I do sometimes wonder what would happen if the ancestry array were
>> writeable. It could be interesting. I haven't thought through the
>> possible pitfalls.
>
> You mean, like Object#become?
Not exactly. As I understand it, #become involves references changing
from one object to another. I'm thinking of something more like:
module M
end
a = Object.new
class << a
ancestors.unshift(M) # essentially same as a.extend(M)
end
> >> I do sometimes wonder what would happen if the ancestry array were
> >> writeable. It could be interesting. I haven't thought through the
> >> possible pitfalls.
...
Would you want to be able to switch ordering too? I wonder what kind
of interesting evil could come of that...
You can play with this in Python. If you modify the __class__ magic
var you can change an object's class in real-time. When I first
discovered this, I posted on a Python list that it seemed like a
sportscar without a seatbelt, and got some very outraged responses
from Python programmers who felt passionately that it was one of the
language's best features. The most memorable response turned my words
around ("sportscar without a speed limit").
On the flipside, I also heard a story from a guy who found this kind
of thing heavily abused in some legacy bioinformatics code in Python,
and he was not happy about it. Objects would wander off into
particular methods and come back home completely transformed. It
sounded very confusing.
