From: Trans <transfire@...>
Date: 2005-04-13T23:44:39+09:00
Subject: Re: help traversing and modifying hash key and value inplace

Robert Klemme wrote:
> There's a subtle thing: you decide whether you traverse on the other
> instance *after* the block got it.  Dunno whether that is what you
want but
> I think I remember the other version decided this based on the
original
> value.

Good catch. Thank you, so:

  def traverse(&b)
    inject({}) do |h,(k,v)|
      nk, nv = b[k,v]
      h[nk] = (Hash === v ? v.traverse(&b) : nv)
      h
    end
  end

> You probably want to leave that out altogether and have the block
> decide this.  In this case traverse would become even simpler.

Hmmm... not sure what "this" refers to. Assuming you mean, whether to
traverse or not. Something like:

  def traverse(&b)
    inject({}) do |h,(k,v)|
      nk, nv = b[k,v]
      h[nk] = nv
      h
    end
  end

Is that right? In that case I wouldn't call it "traverse" though --more
like a hash verion of collect. Actually I think I already have that in
the libs as Enumerable#build_hash.

> Ah, and traverse will crash for recursive structures.

Should I go through the complexity of preventing that? Well, at very
least I will note it in the docs.

Thanks robert,
T.