From: Robert Klemme <shortcutter@...>
Date: 2007-08-20T18:06:28+09:00
Subject: Re: Emulating a Groovy feature?

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