Re: [boost] RE: Serialization Library Review

[Matthias Troyer]

On Monday, November 18, 2002, at 01:04 PM, Jeff Garland wrote:

Let me give one example: we store parameters in a class

typedef std::map<std::string,std::string> ParameterMap

...

If instead of typdef-ing ParameterMap as a std::map, I derive
ParameterMap from it then I can easily write a save and load function
to write and read that output. Thus XML can be included.

There is however the problem that I cannot just write

for (ParameterMap::const_iterator it=m.begin();it!=m.end();++it)
   ar << *it;

since the default serializing of a std::pair does not give my my
PARAMETER element above. Instead I have to write things explicitly:

for (ParameterMap::const_iterator it=m.begin();it!=m.end();++it)
   ar << "<PARAMETER name="\"" << it->first
    << "\">" << it->second << "</PARAMETER>\n";

and reading is more involved.

Well, if this can't be done in a general fashion so that you
don't have to be aware of the 'ParameterMap' in the archive
code then the serialization design is broken.  That's not to
say that the XML backend might not need additional information
that is not normally supplied by the framework.  For example, a
mapping between the type info and the XML element name.

The problem here is that the way you want to serialize a std::pair<std::string,std::string> into XML might depend on the context. Sure, we can design an XML schema that is not context dependent, but most XML schemas are application specific and the way to serialize the data IS context sensitive.

For me XML I/O of class data using an application specific schema is a completely different application than just serializing a class object for persistent storage or transmission to another process. I don't think that any serialization library will be able to accomodate the variety of XML schemas that a user could come up with and still be able to factorize the output into context-insensitive serializations of all classes. See just my example above: the way I serialize the std::pair into XML is very application-specific and I might have other occurences of std::pair that should be serialized differently.

Nevertheless, if you want XML, surely we can wrap the text archive between XML tags to get an XML file, but what is the point of that?

Matthias

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