Re: [boost] [Boost Review] Property Tree Library

From: Gennadiy Rozental (gennadiy.rozental_at_[hidden])
Date: 2006-04-21 22:33:32

"Marcin Kalicinski" <kalita_at_[hidden]> wrote in message 
news:e2bjmg$i92$1_at_sea.gmane.org...
>>> The biggest virtue of property_tree is easy to use interface. If we try 
>>> to make generic tree of it, it will be compromised. This should not 
>>> happen, because people will then prefer to use Expat or MSXML instead.
>>
>> Could you clarify (with details) how is it easier then alternatives?
>
> I assume that by alternatives you mean above mentioned Expat and MSXML?

No, of course. I mean why do I need this half baked property_tree as another 
data structure?

> First, property_tree supports more formats, not just XML.

Property tree supports nothing in itself. It's just a data structure. You 
have parsers that produce property tree out of different sources. But you 
mat as well produce maps or something else. Here for example All that I need 
to do to "implement" similar functionality as your property tree:

// Data structure itself
template<typename ValueType,typename KeyType>
struct Node;

template<typename ValueType,typename KeyType>
struct ptree_gen {
    typedef std::pair<KeyType,Node<ValueType,KeyType> > mi_value;
    typedef multi_index<mi_value, indexed_by<...> > type;
};

template<typename ValueType,typename KeyType>
struct Node {
    ValueType v;
    ptree_gen<ValueType,KeyType>::type children;
};

// serilization support
template<class Archive,typename ValueType,typename KeyType>
void serialize(Archive & ar, Node<ValueType,KeyType>& n, const unsigned int 
version)
{
    ar & n.v;
    ar & n.children;
}

// some access methods
template<typename ValueType,typename KeyType>
ValueType const&
get( string const& keys, ptree_gen<ValueType,KeyType>::type const& src )
{
   std::pait<string,string> sk = split( keys, "." );

   Node const& N = src.find( sk.first );

   return sk.second.empty() ? N.v : get( sk.second, N.children );
}

Use it like this:

ptree_gen<string,string>::type PT;

boost::archive::text_iarchive ia( std::ifstream ifs("filename") );

ia >> PT;

string value = get( "a.b.c.d", PT );

Now tell me how property_tree interface is easier? And what is the value in 
50k of Code you need to implement this data tructure.

Gennadiy