[pclasses-devel] stupid s11n tricks: converting P types to STL equivalents

[stephan b. <st...@s1...>]

Yo!

One of the most interesting tricks serialization gives is the ability to 
"cast" between "similar" types. For example, casting a list<int> to a 
vector<double *>. Here's a demonstration showing how to convert a 
SimplePropertyStore to or from a std::map<string,string>:


First we have to tell s11n to use a proxy for map<string,string> which 
is compatible with the proxy for SimplePropertyStore. i happen to know 
which proxy SPS uses, so we can use the same one. We do that with this 
registration code (called from our client app):


#define PS11N_TYPE std::map<std::string,std::string>
#define PS11N_TYPE_NAME "map"
#define \
    PS11N_SERIALIZE_FUNCTOR \
    ::P::s11n::map::streamable_map_serializable_proxy
#include <pclasses/SIO/RegisterSerializable.h>


SPS is mostly std::map compliant, and uses that same proxy:
see src/SIO/Proxy/SimplePropertyStore_s11n.h

Yes, the exact same proxy can de/serialize both SPS and a std::map (and 
a std::multimap... *any* map-compliant type... even maps of maps of 
maps of pointers to maps).

Now we create a SPS:

	SimplePropertyStore m;

	m["fred"] = "wilma";
	m["barney"] = "betty";
	m["days_in_december"] = 31;
	m["days_in_february"] = 28.5;
	m["the_letter_a"] = 'a';
	save( m, std::cout );

And cast it to a std::map:

	typedef std::map<std::string,std::string> OtherMap;
	OtherMap m2;
	if( ! s11nCast( m, m2 ) )
	{
		CERR << "Map conversion failed!\n";
		return 1;
	}
	save( m2, std::cout );

Outputs:


<!DOCTYPE s11n::io::expat_serializer>
<s11n_node class="P::Util::SimplePropertyStore">
        <barney>betty</barney>
        <days_in_december>31</days_in_december>
        <days_in_february>28.500000</days_in_february>
        <fred>wilma</fred>
        <the_letter_a>a</the_letter_a>
</s11n_node>
SimplePropertyStoreTest.cpp:54 : s11nCast() to map<string,string>:
<!DOCTYPE s11n::io::expat_serializer>
<s11n_node class="map">
        <barney>betty</barney>
        <days_in_december>31</days_in_december>
        <days_in_february>28.500000</days_in_february>
        <fred>wilma</fred>
        <the_letter_a>a</the_letter_a>
</s11n_node>


This type of casting essentially works for any types which use 
"compatible" de/serialization algos. That means, they use algos which 
structure their serialized data identically.


-- 
----- st...@s1...   http://s11n.net
"...pleasure is a grace and is not obedient to the commands
of the will." -- Alan W. Watts