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  1. #include <type_traits>
  2. #include <iostream>
  3. struct A {
  4.   static constexpr unsigned int bar = 20;
  5.  
  6. };
  7.  
  8. struct B {
  9.  
  10. };
  11.  
  12.  
  13. template <typename T,typename=void>
  14. struct getBar {
  15.   static constexpr unsigned int bar = 0;
  16. };
  17.  
  18. template <typename T>
  19. struct getBar<T,std::void_t<decltype(T::bar)>> {
  20.   static constexpr unsigned int bar =  T::bar;
  21. };
  22.  
  23. int main() {
  24.   std::cout << getBar<A>::bar << std::endl; // Expect 20
  25.   std::cout << getBar<B>::bar << std::endl; //Expect 0
  26. }
Success #stdin #stdout 0s 15232KB
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stdin
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Standard input is empty
stdout
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20
0
https://ideone.com/NwxVUu
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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