imathexceptions.cc

#include <iostream>
  
// traits to define which version is used
struct throwexceptions{};
struct dontthrowexceptions{};

const throwexceptions Throw; 

template<typename T> class Bob
{
  public:

  //
  // throwing version with 'opt-in' parameter 
  //
  void invert(const throwexceptions& state = Throw)
  {
          std::cerr << "throwing\n";
          throw 1;
  }

  //
  // non-throwing version with 'opt-out' parameter
  //
  inline void invert(const dontthrowexceptions&) noexcept
  {
        std::cerr << "not throwing\n";
  }
  T lighter;
  T darker;
};
int main(void)
{
        Bob<int> b;

        try
        {
          b.invert(); // throw exception
        } catch(...) { }

        b.invert( dontthrowexceptions() );

        //
        // decide at compile-time whether to throw exceptions
        //
        typedef throwexceptions shouldThrow;
        b.invert( shouldThrow() );
}