Re: [libxml++] Adding STL-container-like methods to Node instead of returning container instance (xmlwrapp)

[Stefan Seefeld <seefeld sympatico ca>]

Murray Cumming wrote:

> 1. Some people don't like changing begin() to children_begin(), because
> it's not really STL-like
> 2. Some people don't like putting only a few STL-like methods in the
> class without adding all of a clearly defined set of them.
> 3. I think that 2. could make the API generally cluttered and unclear.
> 4. I suggested an auxillary class instead to solve the problem of 3.
> 5. Someone needs to look at xmlwrapp to see what it does for this.
>
> Also, could you repeat why you think this API addition is necessary. I
> think you have said so already, but it's lost in the sea of messages.
>
> Please tell us your thoughts about these points. I leave it to you to
> investigate xmlwrapp because you are the author of this API change and
> you are the one who cares about adding it at all. If we do not resolve
> this soon then I will suggest again that we revert the stuff so far.

ok, here is my summary:

it seems we are converging towards the following:

class Node
{
public:
  NodeList get_children();
  NodeList get_attributes();
  //...the rest
};

class NodeList
{
public:
  class iterator;
  class const_iterator;
  iterator begin();
  //...and the rest
};

This looks quite similar to our current approach (at least as far
as the Node API itself goes). The issue I try to resolve is that
'NodeList' was a list, and so you had to copy all child-node pointers
into it to return it. Quite a waste.

With my proposed NodeList class (which will comply to STL API), only
a single xmlNode pointer needs to be copied, as the 'iterator' now
can be implemented in terms of libxml2's internal linked list structure,
not as an iterator over a std::list. That's the main benefit.

There is one remaining issue: we'd need a 'ConstNodeList' type that
provides read-only access to the children. If you hold a const
node reference, you shouldn't access child nodes in r/w mode, i.e
the corresponding 'get_children() const;' method shouldn't return
a NodeList, as you get r/w access with that.
(The issue exists since we don't return a reference to an internal
container, but a new one, so we can't restrict access).

Finally, the xmlwrapp does use the approach I originally sugested:
the Node class itself provides iterators. However, it uses 'begin()'
and 'end()' instead of 'children_begin()' and 'children_end()', but
returns attributes via a separate container (wrapper).

Stefan