Is metaprogramming useful?

[Georg Wrede]

renoX wrote:
> Back on the subject of metaprogamming, one thing which makes me cautious about
> metaprogramming is debugging: when there is a problem debugging generated code is
> a nightmare usually..

It's not metaprogramming itself, it's the bad implementations that make 
it hard.

If we had Perfect Metaprogramming(TM) in D, then I could do the following:

   I'm coding some stuff and I notice that what I'd really want
   is a new keyword, "unless", that would make it so much easier
   for me to write this application clearly. I decide to create it.

   I want to use it like this

     unless (fullMoonTonight) { doRegularStuff() }

   So, to create such a thing in D, I'd write something like

     define("unless", "(", BooleanExpression, ")", BlockStatement)
     {
       if(!BooleanExpression) BlockSTatement;
     }

Now, if I'd made errors in writing the meta code, then the compiler 
would error me, of course. No biggie. And since the D compiler would 
understand what's going on (as opposed to the C preprosessor or 
compiler), the error messages would be what we're used to in D.

Later, when I actually use the "unless" construct, again the error 
messages would be normal because D now understands what "unless" is all 
about.

---

People say GC has to be slow, but that is mostly because it used to only 
exist in languages that were slow to begin with (and badly implemented).

The same thing with metaprogramming. C++ has given it such a bad rep, 
it'll take years before folks learn away from their fears.