Template class with dispatched properties

[Ross Hays]

Okay here is something I was hoping for some general 
clarification on related to this and maybe you can help me sort 
some things out.

The opDispatch method has a template parameter of string 
fieldName. In C++, templates are actually compiled so each 
different use of a template class is compiled into its own thing. 
With D, if this is the case I imagine I would not be able to 
access the template parameter of string? If I can then why does 
it need to be a template parameter at all and not a normal 
parameter.