compile time loops

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Nope, it’s not directly possible. Template metaprogramming is a pure functional language. Every value or type defined through it are immutable. A loop inherently requires mutable variables (Repeatedly test some condition until X happens, then exit the loop).

Instead, you would typically rely on recursion. (Instantiate this template with a different template parameter each time, until you reach some terminating condition).

However, that can solve all the same problems as a loop could.

Edit: Here’s a quick example, computing the factorial of N using recursion at compile-time:

template <int N>
struct fac {
  enum { value = N * fac<N-1>::value };
};

template <>
struct fac<0> {
  enum { value = 1 };
};

int main() {
  assert(fac<4>::value == 24);
}

Template metaprogramming in C++ is a Turing-complete language, so as long as you don’t run into various internal compiler limits, you can solve basically any problem with it.

However, for practical purposes, it may be worth investigating libraries like Boost.MPL, which contains a large number of data structures and algorithms which simplify a lot of metaprogramming tasks.

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