how to reset and how to undefine a class

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Adriano Mitre

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Oct 30, 2006, 12:15:37 AM10/30/06
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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/.

Wilson Bilkovich

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Oct 30, 2006, 12:24:28 AM10/30/06
to

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.

Trans

unread,
Oct 30, 2006, 7:17:46 AM10/30/06
to

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.

Trans

unread,
Oct 30, 2006, 7:22:22 AM10/30/06
to

s/subclass/superclass/

T.

Ross Bamford

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Oct 30, 2006, 9:01:14 AM10/30/06
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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)

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


Trans

unread,
Oct 30, 2006, 1:03:38 PM10/30/06
to

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

T.


Dido Sevilla

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Oct 30, 2006, 8:52:19 PM10/30/06
to
On 10/30/06, Adriano Mitre <adrian...@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.

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)

Adriano Mitre

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Nov 7, 2006, 5:06:19 AM11/7/06
to
> 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.

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