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From Bill Horsman <b...@logicalcobwebs.co.uk>
Subject Re: [PATCH] Re: [jexl] - checking for unresolved variables
Date Tue, 13 Jan 2004 21:23:59 GMT
On Tue, 2004-01-13 at 17:22, Bill Horsman wrote:

> (Yet) another solution:
> 
> Get the JexlContext to track which variables it was asked for. Note
> which ones were known and which were not known. Then you can ask
> JexlContext for the list at the end. 

I got so enthused by this idea that I decided to just do it. There is a
new method on Expression:

    CheckResults check(JexlContext context) throws Exception;

And CheckResults contains:

    Object getAnswer();
    String[] getKnownVariables();
    String[] getUnknownVariables();
    String[] getUsedVariables();

(It's documented better in the patch).

Good things: 

It doesn't break the current API

It gives more information than before: a list of all the unknown
variables (not just the first one encountered), and a list of all the
used variables (this is a nice to have for my current app)

Bad things:

It needs to clone the JexlContext to make it thread-safe. This is done
transparently, but it might effect performance. But then again, I don't
think it's significant. (Actually, as I write this I realise that it
doesn't need to clone it - just wrap it. But the shallow clone of Map is
not too lengthy anyway).

It's not a simple configuration change to make it lenient or strict. You
need to call a different method (check instead of evaluate). I suppose
you could make evaluate do something similar (and just throw an
exception that contained the CheckResults or something).

The patch is an tar archive because I still haven't found a way of
bundling the new files in the patch file. The archive contains two new
Java files and the patch file.

- Bill

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