gistfile1.rb

# A module (for including into the core Ruby Hash class) which performs deep merging,
# but only replaces a value if the replacement value is not nil.
# Operates on object references: friendly_deep_merge!, or copies: friendly_deep_merge
# Also does reverse merging; a hash can be updated only if its own values aren't nil.
module FriendlyDeepMerge
  
  def friendly_deep_merge(hash)
    target = dup
    hash.keys.each do |key|
      if hash[key].is_a? Hash and self[key].is_a? Hash
        target[key] = target[key].friendly_deep_merge(hash[key])
        next
      end
      target[key] = hash[key] unless hash[key].nil?
    end
    target
  end
  
  def friendly_deep_merge!(second)
    second.each_pair do |k,v|
      if self[k].is_a?(Hash) and second[k].is_a?(Hash)
        self[k].friendly_deep_merge!(second[k])
      else
        self[k] = second[k] unless second[k].nil?
      end
    end
  end
  
  def reverse_friendly_deep_merge(other_hash)
    other_hash.friendly_deep_merge(self)
  end
  
  def reverse_friendly_deep_merge!(other_hash)
    replace(reverse_friendly_deep_merge(other_hash))
  end
  
end