From: "Daniel Schüle" <uval@...>
Date: 2005-11-07T00:37:11+09:00
Subject: Re: what does --can't define singleton method-- mean?

Sean O'Halpin wrote:
> On 11/6/05, Daniel Sch�le <uval@rz.uni-karlsruhe.de> wrote:
> 
>>irb(main):014:0* class << Complex
> 
> 
> You're using the wrong syntax here. To re-open a class, just use
> normal class definition syntax:
> 
> class Complex
>   def angle
>     arg/Math::PI*180.0
>   end
> end

I found out that I also can use

Complex.class_eval do
	def angle
		arg / Math::PI * 180
	end
end

this would "update" the method for all instances of Complex class

class << Complex
def angle; "angle"; end
end

would create singleton_method for Complex class itself
Complex.angle => "angle"

what is the advantage or typical use of having singleton method for a class?
I could imagine that since Complex is a Class it has some inherited 
methods from it .. and singleton method would belong only to Complex
nevertheless I can't find scenarious where I could use it
but I am a newbee

thanks to all for your replies

Daniel