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remaining problem w/ dyn var scoping, as proposed (and

Subject: remaining problem w/ dyn var scoping, as proposed (and solution?)
From: "Matt G." <matt_g_@xxxxxxxxxxx>
Date: Thu, 03 Jan 2002 09:12:02
 remaining problem w/ dyn var scoping
I've actually struggled with the use case put forth as the need for dynamic variable scoping. One approach I used to deal with having to add a new parameter, that I wanted passed through to one of my call-backs, was to add an entity reference to all the templates in my stylesheet library. Unfortunately, this does mean that you can't treat the stylesheet library as a black box. However, it made it easy to extend.

I'm just mentioning that as a suggestion to those who may also have to face this problem with an XSLT 1.0 processor (which means you can't use the node-set trick).

Despite having faced this very problem, myself, I didn't like the idea of dynamic-scoping, at first. After I started to see that most of the associated risks could be mitigated or eliminated, I started to warm up to the idea. However, I've spotted one more vulnerability in Dr. Schadow's proposal: namespace collisions among dynamically-scoped variables. What it really comes down to is that two scopes (lexical vs. dynamic) aren't enough. That's not an impossible problem to fix, however. In fact, I think the solution is quite straight-forward. Rather than <parameter scope="dynamic>/> how about using the value of the scope attribute (if present) to be treated as the name of a scope? This allows you to really treat a stylesheet library as a black box (even if it uses several stylesheet libraries, itself), without risking mucking with its inner workings via dynamic-variable namespace collisions.

In fact, I was even thinking that a template which accepts a dynamic variable as dynamic should terminate its scope (i.e. it doesn't get passed down to the next tier of the call-tree, if not done explicitly), by default. However, if the scopes are named, I don't see any advantage to doing this, unless the same template library is used at multiple places in a single call-stack (wait... maybe that's reason enough to do it).

Thanks for considering my suggestion. BTW, XSLT/XPath 2.0 is looking very promising. Cheers to everyone involved!

Matthew Gruenke

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