meta/sqrt4.hpp

The following code example is taken from the book
C++ Templates - The Complete Guide
by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
© Copyright David Vandevoorde and Nicolai M. Josuttis 2002


#ifndef SQRT_HPP
#define SQRT_HPP

#include "ifthenelse.hpp"

// template to yield template argument as result
template<int N>
class Value {
  public:
    enum { result = N };
};

// template to compute sqrt(N) via iteration
template <int N, int I=1>
class Sqrt {
  public:
    // instantiate next step or result type as branch
    typedef typename IfThenElse<(I*I<N),
                                Sqrt<N,I+1>,
                                Value<I>
                               >::ResultT
            SubT;

    // use the result of branch type
    enum { result = SubT::result };
};

#endif // SQRT_HPP