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

From: Stefan Seefeld (seefeld_at_[hidden])
Date: 2003-06-26 12:32:32

Hamish Mackenzie wrote:
> On Thu, 2003-06-26 at 16:04, Stefan Seefeld wrote:
> 
>>I don't really understand why we need three different classes to
>>manage documents. In particular I don't understand why you provide
>>a 'document_ptr' that is a wrapper around document_ref.
> 
> 
> The document_ref and document_ptr would only be used when a non owning
> reference or pointer is required.  Even then you could use
> dom::document * and dom::document & instead in most cases.
> 
> One big difference between a reference and a pointer is that a reference
> must contain a valid non null value.

ok, but are these types really needed ?

My current proposal only provides dom::document_ptr, and I use implicit
refcounting on the underlying document tree. It seems to work quite
fine. I provide a bool operator () that tells me whether the
document_ptr is referring to a document or not.

> dom::document_ref doc1; // Error
> dom::document_ref doc2( 0 ); // Error
> dom::document_ptr doc3; // Ok
> dom::document_ptr doc4( 0 ); // Ok
> 
> This means you do not have to check references for null values.  A
> pointer can be useful if you wish to be able to delay initialisation or
> if an value is optional.
> 
> void some_function( document_ref doc ); // You must pass a doc
> void some_function( document_ptr doc ); // You could pass 0

ok, I can see that as useful.

>>And I don't use a 'document' class, as that is managed implicitely
>>by my dom::document_ptr:
>>
>>dom::document_ptr document; // create new document;
>>dom::document_ptr doc(document); // create second reference to it
>>dom::document_ptr doc2 = document.clone(); // clone it, i.e. make deep
>>                                               copy
> 
> 
> This is not consistent with the standard library or C++ in general.  It
> will seem strange that the pointer class
> 1) Does not require dereferencing

would you say the same if the class name was spelled 'document_ref'
instead ?

> 2) Contains a valid and non null value after default construction

right, see my followup post to that mail.

> 3) Has a constructor such as document_ptr( "config.xml" )
> 4) Has member functions such as write_to_file
> 
> The alternative would allow both...
> 
> boost::shared_ptr< dom::document > doc( new dom::document() );
> boost::shared_ptr< dom::document > doc1( doc );
> dom::document doc2( *doc1 );
> 
> and if the 'doc1' reference was non-owning...
> 
> dom::document doc();  // Create new doc
> dom::document & doc1( doc ); // Second reference
> dom::document doc2( doc1 );  // Deep copy

right, but given such an approach, what would nodes return in their
'parent()' method ?

Regards,
                Stefan