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C++ Type erased dispatch - or whatever
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#include <cstdio> | |
#include <functional> | |
#include <string> | |
#if __cplusplus <= 201200L | |
namespace std { | |
// index_sequence | |
template <std::size_t...> struct index_sequence {}; | |
template <std::size_t N, std::size_t... Is> | |
struct make_index_sequence : make_index_sequence<N - 1, N - 1, Is...> {}; | |
template <std::size_t... Is> | |
struct make_index_sequence<0u, Is...> : index_sequence<Is...> { using type = index_sequence<Is...>; }; | |
}; | |
#endif | |
// Non template, type erased base class | |
struct FunctionCaller { | |
virtual int call() = 0; | |
// getArg is the problem specific bits, these are just dummy implementations | |
template <class T> T getArg(int index, T*); | |
std::string getArg(int index, std::string *) { | |
return "yay"; | |
} | |
int getArg(int index, int*) { | |
return index; | |
} | |
}; | |
template<typename... X> struct FunctionCallerFunctor; | |
// Deal with Functors/Lambdas | |
template <class STATE, class FX, class RET, class... ARGS> struct FunctionCallerFunctor<STATE, FX, RET (FX::*)(ARGS...) const> : public FunctionCaller { | |
FunctionCallerFunctor(STATE *state, FX f) : state(state), func(f) { | |
} | |
template <size_t ... A> RET apply(std::index_sequence<A...>) { | |
return func(FunctionCaller::getArg(A, (ARGS*)nullptr)...); | |
} | |
int call() override { | |
apply(std::make_index_sequence<sizeof...(ARGS)>()); | |
return 0; | |
} | |
FX func; | |
STATE *state; | |
}; | |
// Deal with member functions | |
template <class CLASS, class RET, class... ARGS> struct FunctionCallerMember : public FunctionCaller { | |
FunctionCallerMember(CLASS *c, RET (CLASS::*f)(ARGS...)) : c(c), func(f) { | |
} | |
template <size_t ... A> RET apply(std::index_sequence<A...>) { | |
return (c->*func)(FunctionCaller::getArg(A, (ARGS*)nullptr)...); | |
} | |
int call() override { | |
apply(std::make_index_sequence<sizeof...(ARGS)>()); | |
return 0; | |
} | |
RET (CLASS::*func)(ARGS...); | |
CLASS *c; | |
}; | |
template <class FX> FunctionCaller* registerFunction(const char *name, FX f) { | |
return new FunctionCallerFunctor<void,FX,decltype(&FX::operator()) >(nullptr, f); | |
} | |
template <class STATE, class FX> FunctionCaller* registerFunction(STATE *state, const char *name, FX f) { | |
return new FunctionCallerFunctor<STATE, FX, decltype(&FX::operator()) >(state, f); | |
} | |
template <class CLASS, class RET, class... ARGS> FunctionCaller* registerFunction(const char *name, CLASS *c, RET (CLASS::*f)(ARGS...)) { | |
return new FunctionCallerMember<CLASS, RET, ARGS...>(c, f); | |
} | |
// | |
struct SomeStuff { | |
int someFunc(int x, int y) { | |
printf("Adding %d and %d\n", x, y); | |
return x+y; | |
} | |
}; | |
int main() { | |
SomeStuff data; | |
FunctionCaller *fc; | |
fc = registerFunction(&data, "testX", [=](int, std::string t, int x) { | |
printf("%s %d\n", t.c_str(), x); | |
}); | |
fc->call(); | |
fc = registerFunction("test", [=](std::string t, int x) { | |
printf("Hello %d\n", x); | |
}); | |
fc->call(); | |
fc = registerFunction("test2", &data, &SomeStuff::someFunc); | |
fc->call(); | |
return 0; | |
} | |
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