How to reset and how to undefine a class

Ruby
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!

2

On 10/30/06, Adriano M. [email protected] wrote:

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.

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.

3

Adriano M. 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

Trans wrote:

Adriano M. 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.

5

Ross B. wrote:

class Song < Object
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.

6

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

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)

7

On 10/30/06, Adriano M. [email protected] 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)

8

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.