From: TRANS <transfire@...>
Date: 2006-04-21T04:55:25+09:00
Subject: Ruby Don't E4X

I began work on an implementation of E4X for Ruby. I decided to tackle
the problem from two ends. I  began with a literal translation of the
Javascript-esque pseudo-code given in the specification in order to
obtain a fully compliant implementation. That will unfortunately take
a long while to complete. But I wanted something I could use
post-haste, so I also created a fresh-thought "lite" version, based on
<a href="http://www.onlamp.com/pub/a/onlamp/2004/08/12/ruby_e4x.html">
Jack Herrington's ONLamp.com article</a>, but now much expanded. I
figure in the course of time, the two versions will meet in the middle
for a very Ruby-esque delivery of E4X.

Well, I like to dream. Truth is Ruby just can't provide suitable
syntax without revision to core. Every alternative I've tried is worse
than not using E4X in the first place. First there's the issue of name
clash with built-in methods and the tag names. Does 'x.class' access
element node &lt;class&gt;...&lt;/class&gt; or  the class Xml? I tried
some variable solutions and settled on a bit of delegation. To get at
these built-ins one first calls a public #self method.

  x.self.class

That's acceptable. We'll manage. But then there's the worse problem of
attributes access. Let's say we have this XML:

  x = %{<frog wartindex="10"><ft:color>green</green></frog>}


Standard E4X attribute access notation is:

  x.@wartindex  #=> 10

<p>The '@' won't fly. Too bad. What alternative is there? Jack
Herrington offers:</p>

  x._wartindex

Well, ick. I mean, it's livable, but underscore methods generally
represent hidden methods, not something to be commonly used.

Then there's ugly problem of Namespaces. The whole call notation
starts to get really shakey since you can't do:

  x.ft:color

I could try to trick it, making 'ft' act like a method passing in the
:color tag. That would be weak though. Parenthesis would come into
play when assigning or calling additional methods againt it.

  x.ft(:color)

Would that make sense? Getting real iffy now. In fact, at this point I
figure we're one step away from saying screw this and using hashes for
all of it.

  x['@wartindex']
  x['ft:color']

Look real nice, even if a little more verbose. And then we can dump
the x.self.class thing too. But then, it's not so much E4X anymore. Is
it?

What do you think? Is E4X important enough to change Ruby? Keep in
mind that full compliance would require some changes anyway since
notions like the following are part of the standard:

  x.@*

  x = <frog wartindex="10"><ft:color>green</green></frog>

Notice there are no "quotation" brackets.

T.