From: Robert Klemme <shortcutter@...>
Date: 2007-08-20T18:07:25+09:00
Subject: Re: Emulating a Groovy feature?

2007/8/20, Robert Klemme <shortcutter@googlemail.com>:
> 2007/8/18, John Wells <lists@sourceillustrated.com>:
> > Guys,
> >
> > There's something called Safe Navigation in Groovy (http://groovy.codehaus.org/Statements#Statements-Safenavigation) that I find very appealing.
> >
> > So, Groovy will allow you to safely walk an object graph, even if that graph has nulls in it (the walk will short circuit):
> >
> > def foo = null
> > def bar = foo?.something?.myMethod()
> > assert bar == null
> >
> > Is there an easy way to hack an equivalent out in Ruby?
>
> Try this in IRB
>
> class Object
>   class Holder
>     def __ref() @ref end
>
>     def initialize(ref,&b)
>       @ref = ref
>       instance_eval(&b)
>     end
>
>     def method_missing(s,*a,&b)
>       @ref = @ref.send(s,*a,&b) rescue nil
>       self
>     end
>   end
>
>   def safe(&b)
>     Holder.new(self,&b).__ref
>   end
> end
> F = Struct.new :name
> f=F.new "foo"
> f.safe { name.size > 10 }
> f.safe { name.xxx }
>
> Not too nice though...
>
> Kind regards
>
> robert

PS: Forgot to mention: you can always use the "rescue" modifier:

x = foo.bar.baz rescue nil