This patch add simple one line constructor to the Poco::Dynamic::Var class to allow using this class with your own VarHolder. These customised implementation can use different storage policy or/and basic types. By example for small strings up to 7+1 bytes you can implement VarHolder without pointer but char storage which effectively saves some bytes on 64bit machines etc.
Simple memory benchmark with 10.000.000 strings with size 7+1 bytes
Benchmark results (64bit linux, gcc 4.6.3):
Plain malloc(string + pointers to each) = 383MB of memory occupied
Standard Var with std::string storage + pointers to each = 839 of memory occupied
Customized Var with embedded char storage + pointers to each = 687 of memory occupied