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  1. #include <type_traits>
  2. #include <iostream>
  3.  
  4. struct test1 {
  5.     void Invoke() {};
  6. };
  7.  
  8. struct test2 {
  9.     template<typename> void Invoke() {};
  10. };
  11.  
  12.  
  13. enum class InvokableKind {
  14.     NOT_INVOKABLE,
  15.     INVOKABLE_FUNCTION,
  16.     INVOKABLE_FUNCTION_TEMPLATE
  17. };
  18.  
  19. template<typename Functor, class Enable = void>
  20. struct get_invokable_kind {
  21.     const static InvokableKind value = InvokableKind::NOT_INVOKABLE;
  22. };
  23.  
  24. template<typename Functor>
  25. struct get_invokable_kind<
  26.   Functor,
  27.   decltype(Functor().Invoke())
  28.   >
  29. {
  30.     const static InvokableKind value = InvokableKind::INVOKABLE_FUNCTION;
  31. };
  32.  
  33. template<typename Functor>
  34. struct get_invokable_kind<
  35.   Functor,
  36.   decltype(Functor().Invoke<void>())
  37.   >
  38. {
  39.     const static InvokableKind value = InvokableKind::INVOKABLE_FUNCTION_TEMPLATE;
  40. };
  41.  
  42.  
  43. int main() {
  44.     using namespace std;
  45.  
  46.     cout << (get_invokable_kind<test1>::value == InvokableKind::INVOKABLE_FUNCTION) << endl;
  47.     cout << (get_invokable_kind<test2>::value == InvokableKind::INVOKABLE_FUNCTION_TEMPLATE) << endl;
  48.  
  49. }
  50.  
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
prog.cpp:37:3: error: template argument 2 is invalid
stdout
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Standard output is empty
https://ideone.com/lN4qoA
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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