Question

What exactly is the difference? It seems like the terms can be used somewhat interchangeably, but reading the wikipedia entry for Objective-c, I came across:

In addition to C’s style of procedural
programming, C++ directly supports
certain forms of object-oriented
programming, generic programming, and
metaprogramming.

in reference to C++. So apparently they’re different?

Answer 1

• Programming: Writing a program that creates, transforms, filters, aggregates and otherwise manipulates data.
• Metaprogramming: Writing a program that creates, transforms, filters, aggregates and otherwise manipulates programs.
• Generic Programming: Writing a program that creates, transforms, filters, aggregates and otherwise manipulates data, but makes only the minimum assumptions about the structure of the data, thus maximizing reuse across a wide range of datatypes.

As was already mentioned in several other answers, the distinction can be confusing in C++, since both Generic Programming and (static/compile time) Metaprogramming are done with Templates. To confuse you even further, Generic Programming in C++ actually uses Metaprogramming to be efficient, i.e. Template Specialization generates specialized (fast) programs from generic ones.

Also note that, as every Lisp programmer knows, code and data are the same thing, so there really is no such thing as “metaprogramming”, it’s all just programming. Again, this is a bit hard to see in C++, since you actually use two completely different programming languages for programming (C++, an imperative, procedural, object-oriented language in the C family) and metaprogramming (Templates, a purely functional “accidental” language somewhere in between pure lambda calculus and Haskell, with butt-ugly syntax, since it was never actually intended to be a programming language.)

Many other languages use the same language for both programming and metaprogramming (e.g. Lisp, Template Haskell, Converge, Smalltalk, Newspeak, Ruby, Ioke, Seph).