[jdom-interest] Re: jdom-interest digest, Vol 1 #188 - 6 msgs

[trebor.a.rude at lmco.com]

	Except for the parts about finding the document, this seems to be
what it's already doing. Consider this case:

Element foo = new Element("foo");
Document doc = new Document(foo);
Element bar = foo.getCopy("bar");

bar.addContent(bar);
foo.addContent(bar);

As near as I can tell, under your model this results in an invalid tree,
because "bar.addContent(bar)" still works, and it really shouldn't (it's
almost certainly not what the programmer intended, and I can't think of any
valid use for such a thing). What do you think?

Trebor A. Rude
trebor.a.rude at lmco.com

> -----Original Message-----
> From:	David W. Smiley [SMTP:dsmiley at mitre.org]
> Sent:	Thursday, August 31, 2000 8:22 AM
> To:	jdom-interest at jdom.org
> Subject:	[jdom-interest] Re: jdom-interest digest, Vol 1 #188 - 6
> msgs
> 
> > I think you're right there's another issue that the bar.addContent(bar)
> > command could cause a corrupted tree if bar doesn't have a parent.  We
> > have logic that an element with an existing parent can't be added to
> > another element (you must remove it from its original parent first) but
> > an element just hovering there could theoretically be added to itself,
> > or to its grandchild or great-grandchild or even its child's child's
> > child's child.  Eliminating the possibility of a loop would require a
> > logic as part of every add that looked at the merge point and walks up
> > the tree to the root making sure you never find yourself in the process.
> 
> Wouldn't the problem go away if we play by the following rules?:
> (1) An element can find its document iff it is an ancestor of that
> document.
> (2) An element cannot be added to another document unless the element to
> be added cannot find its document nor its parent.
> 
> To go about implementing these rules...
> (1) clone/copy will return the copy such that it has no parent and
> cannot find its document
> (2) removing an element works like clone/copy except that it's the same
> instance
> (3) adding an element must check that the element has no parent and
> cannot find its document
> (4) the implementation of the element need not necessarily have the
> reference to the document itself; just to a parent element.  By
> traversing to parents until the parent is an instance of a document (or
> rootElement == true depending on how this works), the element can be
> considered bound to a document.
> 
> To maintain these rules, the list returned from getChildren() should be
> smart to check for these constraints.
> 
> -- David Smiley
> 
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