From: Stefano Crocco <stefano.crocco@...>
Date: 2008-02-20T21:43:09+09:00
Subject: Re: instance_eval problem

Alle Wednesday 20 February 2008, bitmox ha scritto:
> Hi,
>
> I' ve got problem with instance_eval.
>
> I tried the following with irb:
> >> obj = "3"
>
> => "3"
>
> >> obj.instance_eval "def a ; puts 'x'; end"
>
> => nil
>
> >> obj.a
>
> x
> => nil
>
> >> obj = 3
>
> => 3
>
> >> obj.instance_eval "def a ; puts 'x'; end"
>
> TypeError: (eval):1:in `irb_binding': no class/module to add method
>         from (irb):31
>
> Why does the instance_eval not work for the Fixnum?
>
> Best regards,
> Thomas

instance_eval works for Fixnums. For example:

(-1).instance_eval("abs")
=> 1

The problem is that you can't define singleton methods for Fixnums (this is 
also true for Floats and Bignums):

x = 1
def x.a
end
=> TypeError: can't define singleton method "a" for Fixnum

Stefano