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  1. #include <iostream>
  2. #include <utility>
  3.  
  4. template<typename T, typename = decltype(std::declval<T>().print_to(std::declval<std::ostream&>()))>
  5. std::ostream &operator<<(std::ostream &s, const T &t) {
  6.     t.print_to(s);
  7.     return s;
  8. }
  9.  
  10. struct foo {
  11.     void print_to(std::ostream &s) const {
  12.         s << "foo";
  13.     }
  14. };
  15.  
  16. int main() {
  17.     std::cout << foo() << "\n";
  18. }
Success #stdin #stdout 0s 15232KB
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stdin
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Standard input is empty
stdout
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foo
https://ideone.com/uLJxac
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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