From: "David A. Black" <dblack@...>
Date: 2007-03-21T22:04:51+09:00
Subject: Re: nil? with block

Hi --

On 3/21/07, Michiel de Mare <merloen@gmail.com> 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. 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:
> 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?

No, I don't like it.  It's unidiomatic for a ?-method to take a block,
and also for a block to serve as a conditional branch.  I'd rather see
it unrolled.  I understand the reasoning behind it, but it ends up
being idiosyncratic in its semantics.


David

-- 
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