How to reset and how to undefine a class

ruby-talk
1

Does any one know how to reset a class in Ruby? Subsequent class
definitions don't replace the original, but are tipically appended to
it.

The following example is typical.

···

#########################
class Song
  def play
    puts "playing..."
  end
end

s = Song.new

class Song
  def stop
    puts "stopped."
  end
end

s.play #=> "playing..."
s.stop #=> "stopped."
#########################

How can I make s.stop produce a NoMethodError, ie., how can I reset Song
class prior to redefining it?

Besides, I would like to know how to undefine Song class, so that
Song.new produce a NameError, i.e., behaving as if it were never
defined.

Thanks!

--
Posted via http://www.ruby-forum.com/.

2

The first question is (a little) straightforward, once you get a
handle on how open Ruby's classes are.
To remove the 'stop' method, 'reopen' the class as you did when adding
'stop' in the first place:

class Song
  undef stop
end

Removing the whole 'Song' constant is a little weirder. There is a
remove_const method, but you have to call it on the thing that
contains the constant you want to remove.
In this case, the thing above Song is Object.

Object.send(:remove_const, :Song)

Sorry for my poor explanation. Hopefully you won't need to do this
very often. I never have. Heh.

···

On 10/30/06, Adriano Mitre <adriano.mitre@gmail.com> wrote:

Does any one know how to reset a class in Ruby? Subsequent class
definitions don't replace the original, but are tipically appended to
it.

The following example is typical.

#########################
class Song
  def play
    puts "playing..."
  end
end

s = Song.new

class Song
  def stop
    puts "stopped."
  end
end

s.play #=> "playing..."
s.stop #=> "stopped."
#########################

How can I make s.stop produce a NoMethodError, ie., how can I reset Song
class prior to redefining it?

Besides, I would like to know how to undefine Song class, so that
Song.new produce a NameError, i.e., behaving as if it were never
defined.

3

Adriano Mitre wrote:

Besides, I would like to know how to undefine Song class, so that
Song.new produce a NameError, i.e., behaving as if it were never
defined.

You can redefine a class entirely by giving it a new subclass.

  class Song < Object
  end

T.

4

All class definitions are constants in the Object class. So by doing
the following:

class Song
end

class Object
remove_const :Song
end

Song.new
NameError: uninitialized constant Song

classes can be undefined. You could also alternatively say:

Object.send(:remove_const, :Song)

···

On 10/30/06, Adriano Mitre <adriano.mitre@gmail.com> wrote:

How can I make s.stop produce a NoMethodError, ie., how can I reset Song
class prior to redefining it?

Besides, I would like to know how to undefine Song class, so that
Song.new produce a NameError, i.e., behaving as if it were never
defined.

5

Trans wrote:

Adriano Mitre wrote:

> Besides, I would like to know how to undefine Song class, so that
> Song.new produce a NameError, i.e., behaving as if it were never
> defined.

You can redefine a class entirely by giving it a new subclass.

  class Song < Object
  end

s/subclass/superclass/

T.

6

The first question is (a little) straightforward, once you get a
handle on how open Ruby's classes are.
To remove the 'stop' method, 'reopen' the class as you did when adding
'stop' in the first place:

class Song
  undef stop
end

I want to remove ("undef") all methods, no only a single one. That is
what I meant with "reset a class".

Removing the whole 'Song' constant is a little weirder. There is a
remove_const method, but you have to call it on the thing that
contains the constant you want to remove.
In this case, the thing above Song is Object.

Object.send(:remove_const, :Song)

Sorry for my poor explanation. Hopefully you won't need to do this
very often. I never have. Heh.

It is not exactly elegant, but indeed I think I won't need it often. I
am inclined to using the "Object.send(:remove_const, :classname)"
solution in both cases, reset and undef.

Thank you very much.

···

--
Posted via http://www.ruby-forum.com/\.

7

I don't get it:

class SomeClass < String
  def ameth(a)
    p a
  end
end

class SomeClass < Object
end

SomeClass.new.ameth(10)

:w !ruby
-:7: superclass mismatch for class SomeClass (TypeError)

···

On Mon, 2006-10-30 at 22:30 +0900, Trans wrote:

Trans wrote:
> Adriano Mitre wrote:
>
> > Besides, I would like to know how to undefine Song class, so that
> > Song.new produce a NameError, i.e., behaving as if it were never
> > defined.
>
> You can redefine a class entirely by giving it a new subclass.
>
> class Song < Object
> end

s/subclass/superclass/

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

8

Ross Bamford wrote:

···

On Mon, 2006-10-30 at 22:30 +0900, Trans wrote:
> Trans wrote:
> > Adriano Mitre wrote:
> >
> > > Besides, I would like to know how to undefine Song class, so that
> > > Song.new produce a NameError, i.e., behaving as if it were never
> > > defined.
> >
> > You can redefine a class entirely by giving it a new subclass.
> >
> > class Song < Object
> > end
>
> s/subclass/superclass/

I don't get it:

class SomeClass < String
  def ameth(a)
    p a
  end
end

class SomeClass < Object
end

SomeClass.new.ameth(10)

:w !ruby
-:7: superclass mismatch for class SomeClass (TypeError)

Hmph.... Looks like Ruby changed this at some point. It used to be able
to do that.

T.