From: Robert Klemme <shortcutter@...>
Date: 2008-03-03T18:38:56+09:00
Subject: Dealing with nil

Hi,

we had frequent discussions about how to make code safely deal with
possible nil values.  I remember having seen various solutions
proposed.  However, I cannot remember having seen this, which just
occurred to me:

class Object
  def nil_safe(fallback = self, &b)
    if nil?
      fallback
    else
      instance_eval(&b)
    end
  end
end

With this, you can do

irb(main):038:0> s=nil
=> nil
irb(main):039:0> s.nil_safe(0) {length}
=> 0
irb(main):040:0> s="foo"
=> "foo"
irb(main):041:0> s.nil_safe(0) {length}
=> 3

Admittedly this is not very pretty.

An alternative definition would be

class Object
  def nil_safe(fallback = self, &b)
    if nil?
      fallback
    else
      yield self
    end
  end
end

And then

irb(main):051:0> s=nil
=> nil
irb(main):052:0> s.nil_safe(0) {|x| x.length}
=> 0
irb(main):053:0> s="foo"
=> "foo"
irb(main):054:0> s.nil_safe(0) {|x| x.length}
=> 3

What do others think?

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end