class Hash

def deep_merge!(other_hash, &block)

Same as +deep_merge+, but modifies +self+. 
def deep_merge!(other_hash, &block)
  merge!(other_hash) do |key, this_val, other_val|
    if this_val.is_a?(Hash) && other_val.is_a?(Hash)
      this_val.deep_merge(other_val, &block)
    elsif block_given?
      block.call(key, this_val, other_val)
    else
      other_val
    end
  end
end