On 28 Apr 2006, at 18:21, David Bovill wrote:
Dave Cragg wrote:
I'd be wary of trapping geturl. This is a handler inside libUrl
that gets called directly by the engine, and it contains some
irregular syntax.
Yes - what is:
return empty with cachedUrl laLoadedUrls[newUrl]
when it is at home?
David, you're only the second person to ask me that question. And the
first on this list. That deserves something, an answer at least.
When I started looking after libUrl, I was told what the syntax did.
When I asked *how* it worked, I was told by Scott Raney, "It's
magic." I left it at that. The alternative was to roll up my pants
legs and make strange incantations.
However, you''ve probably noticed that engine calls can return
something different in both the "it" variable and "the result".
(e.g. read from file etc.) But you can't make your own handlers
behave that way. "get url" (and similar calls) were once handled
inside the engine. When it was decided to do the http and ftp
routines though a script library, I guess some trickery was required
to make sure the engine calls still worked as before.
In addition to dealing with "it" and "the result", the syntax
performs another piece of magic. libUrl stores the data returned from
url calls in a script local array. For "get url" calls, it has to
return the data and empty out the data from the array. If you've ever
had to do this from you own script library, you'll know you normally
have to first copy the data from the script local to a handler local,
then delete the script local, and then return the data. For large
chunks of data, that's a lot of data copying. libUrl is privileged in
having the script local emptied for it by the engine after it
returns. However, as "load" has to preserve the data, the "cachedurl"
part of the syntax lets the engine know whether it should clear the
script local or not.
You did ask. :-)
Cheers
Dave
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