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From "Leo Sutic" <>
Subject RE: [RT] polymorphism and hotswapping
Date Fri, 09 Apr 2004 20:27:01 GMT

> From: Stefano Mazzocchi [] 
> People,
> first of all, I apologize if I sounded somewhat harsh at time in the 
> past two weeks. It's been a hell of a time, 8 hour-long meeting in 
> highly political places (semantic web + jcp) and, boy, I didn't have 
> enough time between things to realize that here I was *not* 
> constantly under attack.

Mate, I'm from Avalon.

I have scar tissue ten meters deep, so I don't feel that much.

>       Do we really need hotswappability?

Personally I have no need for it. The code is complex, and I am always
a bit suspicious of relying on complex code. I also don't need to keep
each individual server running all the time (can take them out of line
one by one).

However, would hotswap be useful during development of blocks? I know
that many Cocoon developers (and webapp developers) like the ability 
to just hit "reload my app" when the make modifications. 

I also like the fact that stylesheets are reloaded when they change 
on disk, so I can make a stylesheet change, hit F5 to reload the page,
and see my change.

If I am going to store skins and resources inside blocks, I would
like to be able to change them without restarting Cocoon.

>       Is it worth the price to pay for the complexity?

The question is if we need to design for hotswap and/or implement it.

I would like us to use the design work Pier has put into the new 
kernel, and make sure that the Cocoon core interfaces *support* 
hotswap. That is, if we later on wanted to add hotswap, we should be
able to do so without changing the Cocoon core interfaces. I 
think we can come up with a client interface that's very easy to
use and addresses the objections to the current interface (i.e. too
ugly client code, too much responsibility on the client, etc.)

But I don't think we have to *implement* hotswap at this moment.
At least not all of it.

The important part is to get blocks running. Hotswap of blocks is
of lower priority, and I don't want the 2.2 to be stuck in development
because hotswap is so hard to implement correctly. Get the blocks
running, and then we can start thinking about how to get hotswap

Finally, when we decide to allow hotswap, I want us to start off
by realizing that we will only cover some cases when hotswap is
possible. There will always be the pathological case where hotswapping
simply isn't posible. But if we can say: "Hotswapping is possible under 
the following three conditions: (1) ... (2) ... (3) ...", then at least
we will have hotswap - probably for 90% of the cases - and I think
the complexity will be manageable.


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