class Hash
  def deep_merge(other_hash, &block)
    dup.deep_merge!(other_hash)
  end

  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

  def slice(*keep_keys)
    h                                              = {}
    keep_keys.each { |key| has_key?(key) && h[key] = fetch(key, nil) }
    h
  end

  def except(*less_keys)
    slice(*keys - less_keys)
  end
end