[libxml++] Preservation of deep const-ness

[Knut A. R. <kn...@if...>]

Hi.

[This is more or less a copy of an email I tried to send to this list 
about a month and a half ago. I am now a member of this list, and hope 
this one gets through.]

I have been using libxml++ for a while and I find its API pleasant
to work with.

When it comes to preservation of const-ness, there appears to be some 
inconsistencies between querying for certain nodes, like pointers to 
parents or siblings, and querying for node collections containing 
pointers to child or attribute nodes.

Currently the const-qualified member functions used for querying for 
children and attributes,

    const NodeList Node::get_children(const Glib::ustring &) const
    const AttributeList Element::get_attributes() const

return STL containers that are const-qualified, while containing 
non-const pointers to the objects (children or attributes). As a 
consequence, client code may modify those objects, undermining the 
const-qualification of the parent node. On the other hand, client code 
is prohibited from modifying siblings or parents, since these pointers 
are const-qualified when returned from the respective const member 
functions.

The enclosed patch contains a proposed fix for this situation.

In addition, the two "find" member functions of Node have been 
overloaded to work with both non-const and const Node objects, returning 
std::vector<Node*> (NodeSet) and std::vector<const Node*> 
(ConstNodeSet), respectively.

The patch also contains an overloaded definition of 
Document::get_root_node(), preserving const from Document to root Element.

I also reorganized the code a bit to get rid of a few const_casts. 
Shared code has been extracted into static *_impl functions.

I assume that some of these changes, if approved, would have to go into 
a new major release, since these API changes are not backward compatible.

Keep up the good work with libxml++! :-)

-- 
Sincerely,
Knut Aksel Røysland