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  1. #include <iostream>
  2.  
  3. struct fact {
  4.     template<typename F> unsigned operator()(unsigned i, F&& f) {
  5.         if(i == 0)
  6.             return 1;
  7.         return i * f(i - 1);
  8.     }
  9. };
  10. struct doubler {
  11.     template<typename F> unsigned operator()(unsigned i, F&& f) {
  12.         return 2 * f(i);
  13.     }
  14. };
  15. template<typename F> struct y_combinator_ref {
  16.     F& f;
  17.     y_combinator_ref(F& farg)
  18.         : f(farg) {}
  19.     template<typename... Args> auto operator()(Args&&... args) 
  20.     -> decltype(f(std::forward<Args>(args)..., y_combinator_ref<F>(f))) {
  21.         return f(std::forward<Args>(args)..., y_combinator_ref<F>(f));
  22.     }
  23. };
  24. template<typename F> struct y_combinator {
  25.     y_combinator(F farg) 
  26.         : f(std::move(farg)) {}
  27.     F f;
  28.     template<typename... Args> auto operator()(Args&&... args) 
  29.     -> decltype(f(std::forward<Args>(args)..., y_combinator_ref<F>(f))) {
  30.         return f(std::forward<Args>(args)..., y_combinator_ref<F>(f));
  31.     }
  32. };
  33. template<typename F> y_combinator<F> y_combine(F f) {
  34.     return y_combinator<F>(std::move(f));
  35. }
  36. int main() {
  37.     auto result = y_combine(fact());
  38.     std::cout << result(5);
  39. }
Compilation error #stdin compilation error #stdout 0s 0KB
comments (?)
stdin 
Standard input is empty
compilation info 
prog.cpp: In function 'int main()':
prog.cpp:28:58: sorry, unimplemented: use of 'type_pack_expansion' in template
prog.cpp:38:26: error: no match for call to '(y_combinator<fact>) (int)'
stdout 
Standard output is empty
https://ideone.com/Qq0tk
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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