From: Christoph <chr_mail@...>
Date: 2004-12-01T10:20:34+09:00
Subject: Re: singleton methods : when are they not permitted?

itsme213 schrieb:

>irb(main):025:0> x = :any
>=> :any
>irb(main):026:0> def x.include(obj); true; end
>TypeError: can't define singleton method "include" for Symbol
>        from (irb):26
>
>Why no singleton methods on Symbol?
>
>Are there other objects that are also not allowed to have singleton methods?
>  
>
Yes you can't define singleton methods for Fixnums either - originally
the answers was all so called "immediate" objects (Fixnums, Symbols
nil,true, and false) which are Object existing outside of the garbage
collector  but Matz implemented special singleton methods (+ singleton
class)  for nil,true and false.  For exmple, both

def nil.fine() end

class << true
    Love = :forever
end

are okay.


Interestingly enough you can define instance variables
for all immediate values - for example

class Object
  def you
    p @you
  end
end

:me.instance_variable_set(:@you, :you)
0.instance_variable_set(:@you, -1)

:me.you  # :you
0.you    # -1

/Christoph