Problems with Factory CXmlCtx, xmlnode class on Solaris

Question

Hi,
I am using Oracle 10g XDK and Iam facing the following problem in Solaris (this works fine in IBM AIX and HP-UX).
CXmlCtx* ctxp = new CXmlCtx();
Factory< CXmlCtx, xmlnode>* fp;
fp = new Factory< CXmlCtx, xmlnode>( ctxp);
parser->domparser = fp->createDOMParser(DOMParCXml, NULL);
The code dumps a core at the 4th line (createDOMParser) function. The code was compiled with SunWSPro compiler /opt/SUNONE8/SUNWspro/bin/cc.
Any pointers to the resolution of this issue will be appreciated.
Thanks

Answer 1

Yes, that is the Factory pattern you describe. The client programs are going to call your createFoo() method and get back an instance of a subclass of Foo. Typically this pattern is used where there is some external entity that determines what subclass will be returned -- for example a system property -- and the client programs call createFoo() with no arguments. In this case reflection is used to create the instance, and your base class does not need to know anything about any subclasses.
However, if your client programs can influence the choice of subclass, then they will have to pass some kind of parameter into createFoo(). At this point, createFoo() requires some decision logic that says "create this, or that, depending on the input parameter". And if that parameter is simply a code that enables the client programs to say "Give me a ChocolateFoo instance", then returning "new ChocolateFoo()" is the most straightforward design. But in this case, why can't the client program do that?
If you don't like the base class having to know about subclasses (and you shouldn't be happy if it does), then you could have a helper class -- FooFactory -- that contains only the static method createFoo(). This class would know about Foo, and about any of its subclasses that it can produce instances of. It's still a maintenance point, no avoiding that, but at least it is off by itself somewhere.