c++ - Partial Specialization for an Integral Constant vs a Type -
is possible specialize template based on whether template argument either type or integral constant? here's example doesn't compile illustrates intent:
#include <cstdio> #include <cstddef> // tag struct struct dynamicsize {}; template<class t, class size> class container; template<class t> class container<t, dynamicsize> { public: container() { std::puts("dynamic size"); } }; template<class t, int size> class container<t, size> { public: container() { std::puts("static size"); } }; int main(int argc, char* argv[]) { container<char, 20> a; container<char, dynamicsize> b; } the eigen library has support matrices of fixed size or runtime determined size , similar this. implementation there template argument integral constant , dynamic tag constant equal -1 i'm curious if there's way.
i think way have container template take type parameter size. it's responsibility of type handle whether it's dynamic or static. i'm thinking details specific type of storage type confined struct types. perhaps following example helpful.
example code
#include <iostream> struct dynamicsize { static const int size = -1; }; template<int size> struct fixedsize { static const int size = size; }; template<class t, class size> class container { public: container() { std::cout << size::size << "\n"; } }; int main() { container<char, fixedsize<20>> a; container<char, dynamicsize> b; return 0; } example output
20 -1 