From: Robert Klemme <shortcutter@...>
Date: 2007-03-21T22:05:15+09:00
Subject: Re: nil? with block

On 21.03.2007 13:51, Michiel de Mare wrote:
> If you have a long chain of method calls, but want to check some
> temporary values for nils, for instance to raise an exception,
> currently the easiest way is with local variables:
> 
> e.g.:
> 
> def zipcode_for_user(user)
>   address = user.personal_data.address
>   raise 'no address!' unless address
>   address.zipcode
> end
> 
> If "nil?" is extended to accept a block, and to return self (for
> Object) and the result of the yield (for NilClass), the following
> notation becomes possible:
> 
> user.personal_data.address.nil?{ raise 'no address!'}.zipcode
> 
> This is more concise, and (I think) also more readable.

Actually I am not sure about readability.  Lines tend to grow pretty 
long that way.  I would probably not use it.  Also keep in mind that you 
will usually get an exception anyway since you're most likely calling a 
method that nil does not support.

 > The flow of
> the program isn't broken by the nil-check. Apart from raise
> statements, it would make sense to use return statements in the
> blocks.
> 
> The implementation is trivial:

... and probably slower than the current implementation as they add 
another boolean check.

> class Object ; def nil? ; block_given? ? self : false ; end ; end
> class NilClass ; def nil? ; block_given? ? yield : true ; end ; end
> 
> Do you think this is a good idea?

I am not so sure.  But you can easily implement this with another method 
name so you don't have to change existing code's behavior.  Also, nil 
values might be just only one reason to throw an exception so I am not 
sure about general usefulness.

Yeah, I know - I'm a conservative skeptic. :-)

Kind regards

	robert