A couple of questions

[Sam Hu]

Thanks.The construct is clear now.

Still leaves Q1,that is ,the *if* expression after the template definition,I want to learn more about the usage,where can I find more information?

and one more question here:
Q4.In the delegate somFnExp:front(),popFront,empty() are all not defined??Anyway it is not an interface ,so why it is allowed?

Thanks for help.
Sam