I wrote an extremely hard and complex program in which I had to use c++ metaprogramming throughout. Not my decision. I do not understand why you could possibly need more metaprogramming than C++ provides. This is a problematic feature to begin with. Not worthless but not worth much. The debugging was difficult. Many problems show up buried in literally thousands of compiler error messages.
That's the issue with C++ metaprogramming. It's so unwieldy and complex that the benefits are difficult to see and the occasions to be worthwhile limited. When the language has better (i.e. simpler) facilities for meta-programming like D, it will open big venues where it makes sense to use it.
It is like programming object oriented in C, it is possible to do but so unwieldy and requiring discipline and verbose boiler plate that there's rarely an occasion where it would be interesting to use. While it is much easier to do in C++ or D or Java (etc.) as they provide the abstractions that makes it useable. C++'s meta-programming facilities are not good enough.
I disagree. Object-oriented programming is very easy in C even though the syntax itself doesn't guide you. Essentially, all C code I write is object-oriented. Perhaps you are thinking about dynamic dispatch which indeed is very annoying to implement correctly in C?
The problem with C++ metaprogramming is not what you can do with it, it's how you do it; which, IME, is always the most convoluted, unsafe way possible.
The “siamese brothers”-ization of templating & metaprogramming is especially painful.
