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
#include "forwardparam.hpp"
#include "functorparam.hpp"
template <typename C, int N>
class BaseMem : public C {
public:
BaseMem(C& c) : C(c) { }
BaseMem(C const& c) : C(c) { }
};
template <typename FO1, typename FO2>
class Composer : private BaseMem<FO1,1>,
private BaseMem<FO2,2> {
public:
// to let it fit in our framework:
enum { NumParams = FO1::NumParams };
typedef typename FO2::ReturnT ReturnT;
// define Param1T, Param2T, and so on
// - use a macro to ease the replication of the parameter type construct
#define ComposeParamT(N) \
typedef typename FunctorParam<FO1, N>::Type Param##N##T
ComposeParamT(1);
ComposeParamT(2);
//...
#undef ComposeParamT
// constructors: initialize function objects
Composer(FO1 const& f1, FO2 const& f2)
: BaseMem<FO1,1>(f1), BaseMem<FO2,2>(f2) {
}
Composer(FO1 const& f1, FO2& f2)
: BaseMem<FO1,1>(f1), BaseMem<FO2,2>(f2) {
}
Composer(FO1& f1, FO2 const& f2)
: BaseMem<FO1,1>(f1), BaseMem<FO2,2>(f2) {
}
Composer(FO1& f1, FO2& f2)
: BaseMem<FO1,1>(f1), BaseMem<FO2,2>(f2) {
}
// ``function call'' for no argument:
ReturnT operator() () {
return BaseMem<FO2,2>::operator()(BaseMem<FO1,1>::operator()());
}
// ``function call'' for one argument:
ReturnT operator() (typename ForwardParamT<Param1T>::Type v1) {
return BaseMem<FO2,2>::operator()(BaseMem<FO1,1>::operator()(v1));
}
// ``function call'' for two arguments:
ReturnT operator() (typename ForwardParamT<Param1T>::Type v1,
typename ForwardParamT<Param2T>::Type v2) {
return BaseMem<FO2,2>::operator()(BaseMem<FO1,1>::operator()(v1, v2));
}
//...
};