From: "David A. Black" <dblack@...>
Date: 2010-08-19T06:29:33+09:00
Subject: Re: Check existence of object and it's property at the same time

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


David

-- 
David A. Black, Senior Developer, Cyrus Innovation Inc.

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