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  1. #include <iostream>
  2. #include <typeinfo>
  3.  
  4. // mapping :: TYPE -> TYPE
  5. // ---------------------------------------------------------
  6. // ?? --> int (default "value")
  7. template<typename X> struct mapping {
  8.   using type = int;
  9. };
  10. // if instead you want it to be undefined for unknown types:
  11. //template<typename X> struct mapping;
  12. // bool --> double
  13. template<> struct mapping<bool> {
  14.   using type = double;
  15. };
  16.  
  17.  
  18.  
  19. // map :: ([T] -> T) -> (T -> T) -> ([T] -> T)
  20. //         "List"       "Mapping"   result "type" (also a "List")
  21. // --------------------------------------------------------
  22. template<template<typename...> class List,
  23.          template<typename> class Mapping>
  24. struct map {
  25.   template<typename... Elements>
  26.   using type = List<typename Mapping<Elements>::type...>;
  27. };
  28.  
  29.  
  30. template<typename...> struct Example {};
  31.  
  32.  
  33.  
  34. template<typename... S>
  35. using MappedExample = map<Example, mapping>::type<S...>;
  36.  
  37. template<typename... S>
  38. MappedExample<S...> f() {
  39.   return MappedExample<S...>{};
  40. }
  41.  
  42.  
  43. int main() {
  44.   std::cout
  45.     << typeid(Example<bool,int,char,double>).name()
  46.     << std::endl
  47.     << typeid(decltype(f<bool, int, char, double>())).name()
  48.     << std::endl;
  49. }
Success #stdin #stdout 0s 15240KB
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7ExampleIJbicdEE
7ExampleIJdiiiEE
https://ideone.com/E9yMCQ
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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