try_scope

try_scope.rb

# Inspired by http://intridea.com/2010/11/2/calling-methods-on-potential-nil-objects-in-rails

class Object
  def try_scope(&block)
    # self is nil if it is called by NilClass object
    block.call(self) if self
  end
end

p ['a', 'b', 'c'].try_scope{|a| a.map{|b| b.capitalize}.map{|b| b.downcase}} # => ["a", "b", "c"]
p nil.try_scope{|a| a.map{|b| b.capitalize}.map{|b| b.downcase}.foo(1)} # => nil
p ['a', 'b', 'c'].try_scope{|a| a.map{|b| b.capitalize}.map{|b| b.foo(1)}} # => NoMethodError: undefined method ‘foo’ for "A":String

# Note:
# The alternative is to use "Black Halls" technique introduced at 
# http://www.pragprog.com/magazines/2010-01/much-ado-about-nothing
#
# class NilClass
#   def method_missing(*); end
# end
#
# This absorbs any errors raised from nil, but this may hinder bugs as mentioned in the article itself.
# By using try_scope{}, you can restrict the use of black halls only to the place you want to apply.
#
# The another argument may be that we should not chain too many methods in general.