From: Mike Stok <mike@...>
Date: 2013-03-09T23:44:12+09:00
Subject: Re: Confusion with unary operator overidding

+ and - can be both unary and binary operators, so there are differently named methods for the different operations.  http://www.rubyinside.com/rubys-unary-operators-and-how-to-redefine-their-functionality-5610.html might be intresting to you .

Hope this helps,

Mike

On 2013-03-09, at 9:07 AM, "Kumar R." <lists@ruby-forum.com> wrote:

> I was trying to learn the operator over-ridding in Ruby. So i used the
> below in my IRB.
> 
>>> class Banner < String
>>> def +
> ?> upcase
>>> end
>>> def -
> ?> downcase
>>> end
>>> end
> => nil
>>> ban = Banner.new("hi")
> => "hi"
>>> +ban
> NoMethodError: undefined method `+@' for "hi":Banner
>        from (irb):22
>        from C:/Ruby193/bin/irb:12:in `<main>'
> 
> Now after seeing the error in the `IRB` i corrected definition of `+`
> and `-` as below, which in turn fixed the code.
> 
>>> class Banner < String
>>> def +@
>>> upcase
>>> end
>>> def -@
>>> downcase
>>> end
>>> end
> => nil
>>> ban = Banner.new("hi")
> => "hi"
>>> +ban
> => "HI"
> 
> But my confusion is with the logical necessity of that `@` operator?
> 
> Again I tried to over-ride `!` as below:
> 
>>> class Banner
>>> def !
>>> reverse
>>> end
>>> end
> => nil
>>> !ban
> => "ih"
>>> not ban
> => "ih"
> 
> But here I didn't need to use that `@` operator.
> 
> Can anyone help me to understand why `@` was needed with `+` and `-` but
> not with `!`?
> 
> Thanks
> 
> -- 
> Posted via http://www.ruby-forum.com/.

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.