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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <utility>
  4.  
  5.     // Utility
  6.     template <typename T, typename Result = void>
  7.     struct enable: std::enable_if< std::is_same<T, std::true_type>::value > {}; 
  8.  
  9.     template <typename T, typename Result = void>
  10.     struct disable: std::enable_if< not std::is_same<T, std::true_type>::value > {}; 
  11.  
  12.     // Hook
  13.     std::false_type has_specific_foo(...);
  14.  
  15.     template <typename T>
  16.     auto foo(T const& t) -> typename disable<decltype(has_specific_foo(t))>::type {
  17.       std::cerr << "Generic case\n";
  18.     }
  19.  
  20.     struct A{};
  21.  
  22.     void foo(A const&) { std::cerr << "A\n"; }
  23.     std::true_type has_specific_foo(A const&);
  24.  
  25.     struct B: A{};
  26.  
  27.     int main() {
  28.       B b;
  29.       foo(b);
  30.     }
Success #stdin #stdout 0s 2824KB
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https://ideone.com/sJbom
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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