From: Alex Stahl <astahl@...5.com>
Date: 2010-08-19T06:21:44+09:00
Subject: Re: Check existence of object and it's property at the same time

I've run into a similar situation before, and found that
short-circuiting in an 'if' statement is inconsistent.

For instance, this will short-circuit and prevent evaluation of
subsequent statements if the first one is false (which is desired
obviously):

unless creds.class.to_s =~ /Hash/ && creds.has_key?("user") && ...


But this won't:

unless creds.instance_of?(Hash) && creds.has_key?("user") && ...


I'd be interested to learn why the first one short-circuits and the
second doesn't.  Anyone have any insight?

Thanks,
Alex


On Wed, 2010-08-18 at 16:09 -0500, Cory Patterson wrote:
> I run into this from time to time and I was wondering if there is a
> cleaner way to do check that an object is not nil and also check a
> property of that object.
> 
> I want to do this:
> 
> if !@member.nil? and @member.is_active?
>   ... do something ...
> else
>   ... do something else ...
> end
> 
> But this obviously raises a no method error if @member is nil.
> 
> I end up having to do:
> 
> if !@member.nil?
>   if @member.is_active?
>     ... do something ...
>   else
>     ... do something else ...
>   end
> end
> 
> I know it isn't that much more verbose, but does ruby have a more
> elegant way of handling this?