From: Stefano Crocco <stefano.crocco@...>
Date: 2008-08-13T01:24:18+09:00
Subject: Re: What's the easiest way to check if param[:x][:y] exists?

On Tuesday 12 August 2008, Joshua Muheim wrote:
> Hi all
>
> In PHP I can simply check whether $param['x']['y'] exists regardless
> whether $param['x'] exists or not.
> In Rails I get a NoMethodError when using
>
> if param[:x][:y]
>   ..
> end
>
> when param[:x] is nil. So I always have to use
>
> if param[:x] and param[:x][:y]
>   ..
> end
>
> but I think that's not very beautiful - think about a case where I have
> to check whether param[:a][:b][:c][:d][:...] exists or not!
>
> Maybe there's a cooler way to do this? ;-)
>
> Thanks
> Josh

You can use the rescue modifier, like this:

if (param[:x][:y] rescue nil)
  ...
end

The expression in brackets will return the value of param[:x][:y] but if 
param[:x][:y] raises an exception derived from StandardError (like 
NoMethodError), the exception will be caught by the rescue modifier, and the 
statement to the right of rescue (nil) will be returned. 

I hope this helps

Stefano