Re: [boost] Re: API Review request: XML API for C++, second round

From: Hamish Mackenzie (hamish_at_[hidden])
Date: 2003-06-27 08:48:15

On Fri, 2003-06-27 at 12:53, Anthony Williams wrote:
> It was meant to be a description of semantics, in terms of a sample
> implementation.
> 
> A node that is not part of a document is a free-standing subtree that needs
> adding to a document. If it is an element, then you can treat it as if it is
> the root node of a document. If it is anything else, then you are more limited
> in what you can do, but then what does it mean to perform an XPath query on a
> PI?
>
> If the underlying API requires that the document is kept alive to keep the
> nodes alive, then the wrapper class must handle this, whilst simulating the
> above semantic description.

If you look in one of my other posts you will see a description of just
that.  The thing that concerns me most about this is

doc.find( path ).parent(); // non null (unless it found the root node)

BUT...

node n( doc.find( path ) );
n.parent();  // User may not expect this to be null
n.document();  // or this

You could have a node_container (or standalone_node) which had no parent
or document methods but otherwise looked like a node.

node_container n( doc.find( path ) );
n.parent();  // compile time error
n.document();  // compile time error

which is good but doesn't really solve the problem...

n.first_child().document();  // null

My preference is that if you want to make a copy of a node you have to
have a new document...

document doc2( doc.find( path ) );

doc2.root().parent(); // null but you would expect that (it's the root)
doc2.root().document();  // non null as you would expect

That way the user can rely on parent() to be non null for all but root
nodes and document() can return a reference since it can never be null.

> > You could copy the libxml2 tree into your own structure but then you are
> > on your own when it comes to higher level things like xpath and xslt.
> 
> I imagined that you would write forwarding functions for the underlying API,
> so when you are given an Xpath query, you pass it on to the underlying API and
> then wrap the result.

Then you would need to keep libxml2 version of the tree too and
synchronise any changes (or rebuild it every time you want to call a
libxml2 function).

-- 
Hamish Mackenzie <hamish_at_[hidden]>