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  1.  #include <iostream>
  2.  
  3. template<typename T> class Foo;
  4.  
  5.  template <typename T>
  6. std::ostream& operator<< (std::ostream& o, const Foo<T>& x);
  7.  
  8.  template<typename T>
  9.  class Foo {
  10.  public:
  11.    Foo(T const& value = T());
  12.    friend std::ostream& operator<< <> (std::ostream& o, const Foo<T>& x);
  13.    //friend std::ostream& ::operator<< (std::ostream& o, const Foo<T>& x);
  14.  private:
  15.    T value_;
  16.  }; 
  17.  
  18.   template<typename T>
  19.  Foo<T>::Foo(T const& value )
  20.    : value_(value)
  21.  { }
  22.  
  23.  template<typename T>
  24.  std::ostream& operator<< (std::ostream& o, const Foo<T>& x)
  25.  { return o << x.value_; } 
  26.  
  27.  int main()
  28.  {
  29.    Foo<int> rhs(2);
  30.    std::cout << rhs;
  31.  }
Success #stdin #stdout 0.01s 2724KB
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stdin 
Standard input is empty
stdout 
2
https://ideone.com/kmIfc
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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