From: Alex Stahl <astahl@...5.com>
Date: 2010-08-19T06:52:44+09:00
Subject: Re: Check existence of object and it's property at the same time

Strange... it was failing before (like a few weeks ago) w/ a
NoMethodError on has_key? when it wasn't a hash.  But trying it again
now works fine as you note.


On Wed, 2010-08-18 at 16:33 -0500, David A. Black wrote:
> On Thu, 19 Aug 2010, David A. Black wrote:
> 
> > Hi --
> >
> > On Thu, 19 Aug 2010, Alex Stahl wrote:
> >
> >> 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") && ...
> >
> > They both short-circuit. Note that the puts("here") statement never gets
> > executed.
> >
> >>> creds = {}
> > => {}
> >>> unless creds.class.to_s =~ /Hash/ && creds.has_key?("user") && 
> >>> puts("here"); 1; end
> > => 1
> >>> unless creds.instance_of?(Hash) && creds.has_key?("user") && puts("here"); 
> >>> 1; end
> > => 1
> 
> (P.S. I've made the second condition fail, rather than the first, but if
> you make creds a non-hash it will short-circuit after the first one.)
>