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  1. #include <list>
  2. #include <iostream>
  3. #include <vector>
  4.  
  5. template <typename T>
  6. struct has_reserve {
  7.  private:
  8.   template <typename U>
  9.   static auto test(U *t) -> decltype(t->reserve(0), std::true_type{});
  10.  
  11.   template <typename>
  12.   static std::false_type test(...);
  13.  
  14.  public:
  15.   static bool constexpr value = decltype(test<T>(nullptr))::value;
  16. };
  17.  
  18. template <typename T>
  19. typename std::enable_if<has_reserve<T>::value, void>::type
  20. reserve(T &object, typename T::size_type n) {
  21.   return object.reserve(n);
  22. }
  23.  
  24. template <typename T>
  25. typename std::enable_if<!has_reserve<T>::value, void>::type
  26. reserve(T &, typename T::size_type) {}
  27.  
  28. int main() {
  29.   std::vector<int> v;
  30.   reserve(v, 3);
  31.   v.push_back(1);
  32.   v.push_back(2);
  33.   v.push_back(3);
  34.   for (auto i : v) std::cout << i << " ";
  35.   std::cout << "\n";
  36.  
  37.   std::list<int> l;
  38.   reserve(l, 3);
  39.   l.push_back(3);
  40.   l.push_back(2);
  41.   l.push_back(1);
  42.   for (auto i : l) std::cout << i << " ";
  43.   std::cout << "\n";
  44. }
Success #stdin #stdout 0s 3272KB
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3 2 1
https://ideone.com/wUt4rD
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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