Loop Unrolling in C++ TMP

loop-unrolling.cc

// Generative Programming: Methods, Techniques and Applications
// Ch.8 Static Metaprogramming in C++
#include <iostream>

using namespace std;

template <int i>
struct aStatement {
  enum { n = i };

  static void exec() { cout << i << endl; }

  typedef aStatement<n + 1> Next;
};

struct aCondition {
  template <class Statement>
  struct Code {
    enum { RET = (Statement::n <= 10) };
  };
};

template <bool condition, class Then, class Else>
struct IF {
  typedef Then RET;
};

// partial specialization
template <class Then, class Else>
struct IF<false, Then, Else> {
  typedef Else RET;
};

struct Stop {
  static void exec(){};
};

template <class Condition, class Statement>
struct WHILE {
  static void exec() {
    IF<Condition::template Code<Statement>::RET, Statement, Stop>::RET::exec();

    typedef typename Statement::Next NewStatement;
    IF<Condition::template Code<Statement>::RET, WHILE<Condition, NewStatement>,
       Stop>::RET::exec();
  }
};

int main() { WHILE<aCondition, aStatement<1>>::exec(); }