Re: [Jsynthlib-devel] XML patch saving....

[Joe E. <jo...@em...>]

Rib Rdb wrote:
> Okay.  Let me explain a little about how the XML parser I built works.
>  The basic idea is that has a list of element names which can have
> child elements.  When it encounters the start tag for one of these
> elements, it starts building an object.
> So if there was an xml file like this:
>
> <patchbasket>
> <patch>
> <author>foo</author>
> </patch>
> </patchbasket>
>   
There's some kind of patch data included, I hope. :) Sysex, maybe?
> The parser would:
> 1) Create a patchbasket object
> 2) create a patch object
> 3) Use introspection to find (and call) a setter (in the patch)
> setAuthor(String) or addAuthor(String)
> 4) Use introspection to find (and call) a setter in the basket class
> setPatch or addPatch which will accept the created patch
> 5) Return the patchbasket object
>   
Okay... this looks good.
> Then each IPatch implementation has to have some sort of a
> write method, plus matching setters.  We should probably have some
> sort of helper for binary data.  The implementation would look
> somthing like this:
>
> void write(XMLWriter xml) {
>   xml.writeProperty("author", self.author);
>   xml.writeBinaryProperty("data", self.sysex);
> }
>
> void setAuthor(String author) { /* ... */ }
> void setData(String data) { self.sysex = XMLTools.decodeBinary(data); }
>   
I'm a little uneasy by the requirement that the "author" in 
writeProperty has to match the "Author" in "setAuthor". First, you have 
to have two dissimilar items (a hard-coded string "something" in a call 
to writeProperty and a method called "setSomething") that have to match. 
Furthermore, if they don't match, your first indication of a problem 
comes *after* the XML file has been written and you're now trying to 
load it.

The second problem is even worse, though. If *you* write an 
implementation of IPatch... then it would have a write() method. Now, 
suppose that *I* come along and write a subclass your implementation. If 
I want the additional data of my subclass saved, then I also have to 
have a write() method. However, if I do that, then *your* write method 
doesn't get called anymore. I'd either have to go look at your class and 
save all of the data elements that *your* write() method was saving 
(imagine what happens when you add/remove some data elements to your 
class without telling me), or I'd have to call "super.write(xml)" any 
time I wrote a write() method of my own.

Either of those solutions would require that the author of the subclass 
have an awareness of the inner workings of the patch-saving system that 
I'm not convinced should be necessary.

I think we can find a slicker way.

- Joe