Enable constructor iff two member functions are present in the passed template type-CodePudding

With this code:

struct MyStructure {
  MyStructure(char* d, int size) {}

  template <typename T>
  MyStructure(T&& rhs) : MyStructure(rhs.data(), rhs.size()) {}
};

How can I only enable the second constructor to be present if the data and size functions are present in whatever object is passed in?

CodePudding user response：

Here is what Sam Varshavchik meant, which should work with C 11:

struct MyStructure {
  MyStructure(char* d, int size) {}

  template <typename T, 
     decltype(static_cast<char*>(std::declval<T &&>().data())) = nullptr,
     decltype(static_cast<int>(std::declval<T &&>().size())) = 0
     >
  MyStructure(T&& rhs) : MyStructure(rhs.data(), rhs.size()) {}
};