running DWT with DDL

John Reimer terminal.node at
Wed May 28 19:02:04 PDT 2008

Hello Tom,

> Perhaps a little background info might be useful. Frank had a few
> rather tricky requirements:
> 1. There is a large library which should be shared across applications
> 2. There are plugins to the library
> 3. Applications must be able to derive classes from the ones in
> plugins
> 4. Plugin implementations may be changed post-deployment. In other
> words, the app may not know the source or binary code of the plugins
> in
> advance.
> 1. itself is a tough issue on Windows, as DLLs are not D - friendly.
> 2, 3, and 4 mean that the application has classes whose code parts are
> not known until the plugins are loaded. While it might be solved with
> some fancy design patterns, it would be nice if the setup worked out
> of
> the box without any hacking around.
> But how can we have an executable that derives from classes whose
> implementation is not known - it's in .di files? As far as I know, one
> can't have incomplete executables on Windows or Linux. (executables
> with unresolved symbols).
> Here's where DDL steps in. There are perhaps more solutions, but we've
> employed a version where there's a 'host' executable that loads the
> application, the lib (and potentially the plugins) dynamically. The
> host links them all together using DDL and then starts the app. As a
> result, we only have one executable (and as Frank said, it can be
> shared across apps) and lots of libs that are loaded thru DDL. As libs
> may be incomplete, all problems are solved right away.

This is great news!  Tom and Frank, thanks for experimenting with this.

I'm looking forward to seeing this option applied creatively to dwt projects 
(and other D projects).  I can see that this sort of plugin architecture 
could prove quite useful for larger dwt apps like poseidon or even application 
"systems" like eclipse (no D equivalent yet).  This may not necessarily be 
useful for small dwt apps, but I'm sure there are a host of opportunities 
for creative use.  Perhaps from OS kernels to high-level plugin systems.

Great work!


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