From: Josh Cheek <josh.cheek@...>
Date: 2011-04-17T01:17:36+09:00
Subject: Re: Get the real object in a Hash key

--0016e64cb1ead1d3cf04a10b7db9
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

On Sat, Apr 16, 2011 at 9:51 AM, I=F1aki Baz Castillo <ibc@aliax.net> wrote=
:

> 2011/4/15 Kevin Mahler <kevin.mahler@yahoo.com>:
> > He has a key. It contains some
> > data. It's not necessarily true that he should duplicate that data in
> > the mapped-to values.
>
> To clarify, my exact case is the following:
>
> I've coded a parser for SIP (similar to HTTP). The parser generates a
> Request object which inherits from Hash, and each SIP request header
> (i.e. "From: sip:alice@example.org") becomes an entry of the hash
> (Request object) as follows:
>
> - The key is "FROM" (capitalized).
> - The value is an Array of strings (a s header can have multiple values).
>
> I need to store the key capitalized for fastest lookup, but I also
> want to store the original header name (which could be "from", "From",
> "frOM" and so).
> So my parser adds an instance variable @real_name within the header
> name string ("FROM").
>
> When I do the lookup of a header in the Request object, I would like
> also to retrieve the key's @real_name, but I've already understood
> that this is only possible if taint the key string before inserting it
> in the hash and use Hash#assoc. This solution is not good for
> performance.
>
> The solution suggested by Robert is adding such information (the
> header original name) as a field in the hash entry value, so instead
> of having:
>
>  request["FROM"]
>  =3D> [ "sip:alice@xample.org ]
>
> I would end with something like:
>
>  request["FROM"]
>  =3D> Struct ( "From", [ "sip:alice@xample.org ] )
>
> The problem this last suggestion introduces is that it breaks the
> existing API and makes more complext for a developer to handle the
> Request class (which should be as easy as handling a Hash).
>
>
> Thanks to both for your comments.
>
> --
> I=F1aki Baz Castillo
> <ibc@aliax.net>
>
>

You don't have to have a hash to implement a hash interface. How about
simply creating your own class that supports the interface you want, but
also the functionality you want. Something like this:



class Request

  Header =3D Struct.new :key , :value

  def self.parse(headers)
    request =3D Request.new
    headers.each_line do |header|
      key, value =3D header.split ": "
      request.add_header key , value.chomp
    end
    request
  end

  def initialize
    @headers =3D Hash.new
  end

  def add_header(key, value)
    @headers[key.upcase] =3D Header[key,value]
  end

  def [](key)
    @headers[key][:value]
  end

  def original(key)
    @headers[key][:key]
  end

end


headers =3D <<HEADER
frOM: sip:alice@example.org
To: sip:brad@example.org
HEADER

request =3D Request.parse headers

request["FROM"]         # =3D> "sip:alice@example.org"
request.original "FROM" # =3D> "frOM"

request["TO"]           # =3D> "sip:brad@example.org"
request.original "TO"   # =3D> "To"

--0016e64cb1ead1d3cf04a10b7db9--