On Feb 6, 12:09     
> Hi there,
>
> we frequently do
>
> ha = Hash.new {|h,k| h[k] = []}
>
> so we can later do
>
> ha[any_key] << anything
>
> Since the idiom is so common, what does everybody think of putting it
> into the standard library:
>
> def Hash.with_arrays
>     > end
>
> While we're at it, we might as well add
>
> def Hash.with_hashes
>     
> end

I've been using the name #autonew for this last one.

Also @Tom Link

  def Hash.with(default=nil)
    begin
      new { | h, k | h[k] = default.dup }
    rescue TypeError
      new(default)  # same as { | h, k | h[k] = default }
    end
  end

T.