Why can't I alias_method :remove_method?

Ruby
1

irb(main):001:0> class Foo
irb(main):002:1> alias_method :old_remove_method, :remove_method
irb(main):003:1> end
NameError: undefined method remove_method' for classFoo’
from (irb):2:in `alias_method’
from (irb):2

But you can call remove_method from within the class, so why can’t you
alias it? What other methods can’t you alias? Or rather, what are the
restrictions/conditions under which you must use alias_method?

2

Hi,

At Thu, 10 Aug 2006 15:46:40 +0900,
Pat M. wrote in [ruby-talk:207490]:

irb(main):001:0> class Foo
irb(main):002:1> alias_method :old_remove_method, :remove_method
irb(main):003:1> end
NameError: undefined method remove_method' for classFoo’
from (irb):2:in `alias_method’
from (irb):2

But you can call remove_method from within the class, so why can’t you
alias it? What other methods can’t you alias? Or rather, what are the
restrictions/conditions under which you must use alias_method?

You can call a singleton method named remove_method which is
inherited from the super class, Module, but you didn’t define
an instance method named remove_method.

You can:

class Foo
class << self
alias_method :old_remove_method, :remove_method
end
end