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  1. #include <unordered_map>
  2. #include <typeinfo>
  3. #include <typeindex>
  4. #include <string>
  5. #include <type_traits>
  6. #include <iostream>
  7. #include <assert.h>
  8. #include <cxxabi.h>
  9. #include <sstream>
  10.  
  11. #include <stdexcept>
  12.  
  13. template <typename Func, Func f>
  14. struct store_func_helper;
  15.  
  16.  
  17. std::string demangle(const std::string& val) {
  18.   int     status;
  19.   char   *realname;
  20.  
  21.   std::string strname = realname = abi::__cxa_demangle(val.c_str(), 0, 0, &status);
  22.   free(realname);	
  23.   return strname;
  24. }
  25.  
  26. // args will be implicitly converted to arg<T>::type before calling function
  27. // default: convert to const Arg
  28. template <typename Arg, typename snifae=void>
  29. struct arg {
  30.   using type = const Arg&;
  31. };
  32.  
  33. // numeric types: convert to double.
  34. template <typename Arg>
  35. struct arg <Arg, typename std::enable_if<std::is_arithmetic<Arg>::value, void>::type> {
  36. 	using type = double;
  37. };
  38.  
  39. // set more special arg types here.
  40.  
  41.  
  42. // Functions stored in the map are first wrapped in a lambda with this signature.
  43. template <typename Ret, typename... Arg>
  44. using func_type = Ret(*)(typename arg<Arg>::type...);
  45.  
  46. class func_map {
  47.   template <typename Func, Func f>
  48.   friend class store_func_helper;
  49.  
  50. public:
  51. template <typename Func, Func f>
  52. void store(const std::string& name){
  53.   store_func_helper<Func, f>::call(this, name );
  54. }
  55.  
  56. template<typename Ret, typename... Args>
  57. Ret call(std::string func, Args... args){
  58.   using new_func_type = func_type<Ret, Args...>;
  59.   auto& mapVal = m_func_map.at(func);  
  60.  
  61.   if (mapVal.second != std::type_index(typeid(new_func_type))){
  62.   	std::ostringstream ss;
  63.   	ss << "Error calling function " << func << ", function type: " 
  64.   	  << demangle(mapVal.second.name()) 
  65.   	  << ", attempted to call with " << demangle(typeid(new_func_type).name());
  66.   	throw std::runtime_error(ss.str());
  67.   }
  68.   auto typeCastedFun = (new_func_type)(mapVal.first);
  69.  
  70.   //args will be implicitly converted to match standardized args
  71.   return typeCastedFun(std::forward<Args>(args)...);
  72. };
  73.  
  74.  
  75.  
  76. private:
  77. std::unordered_map<std::string, std::pair<void(*)(),std::type_index> > m_func_map;
  78. };
  79.  
  80. #define FUNC_MAP_STORE(map, func) (map).store<decltype(&func),&func>(#func);
  81.  
  82.   template <typename Ret, typename... Args, Ret(*f)(Args...)>
  83.   struct store_func_helper<Ret(*)(Args...), f> {
  84.     static void call (func_map* map, const std::string& name) {
  85.       using new_func_type = func_type<Ret, Args...>;
  86.  
  87.       // add a wrapper function, which takes standardized args.
  88.       new_func_type lambda = [](typename arg<Args>::type... args) -> Ret {
  89.         return (*f)(args...);
  90.       };
  91.       map->m_func_map.insert(std::make_pair(
  92.         name, 
  93.         std::make_pair((void(*)()) lambda, std::type_index(typeid(lambda)))
  94.         ));
  95.     }
  96.   };
  97.  
  98. //examples
  99.  
  100. long add (int i, long j){
  101.   return i + j;
  102. }
  103.  
  104. int total_size(std::string arg1, const std::string& arg2) {
  105. 	return arg1.size() + arg2.size();
  106. }
  107.  
  108. int  main() {
  109.   func_map map;
  110.   FUNC_MAP_STORE(map, total_size);
  111.   FUNC_MAP_STORE(map, add);
  112.  
  113.   std::string arg1="hello", arg2="world";
  114.   std::cout << "total_size: "  << map.call<int>("total_size", arg1, arg2) << std::endl;
  115.   std::cout << "add: " << map.call<long>("add", 3, 4) << std::endl;
  116. }
  117.  
  118.  
  119.  
Success #stdin #stdout 0s 15248KB
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Standard input is empty
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total_size: 10
add: 7
https://ideone.com/R7TP96
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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