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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. template< class T >
  6. class foo
  7. {
  8. public:
  9.    T _value;
  10.    foo() : _value() {}
  11.  
  12.    template <class U>
  13.    foo(const foo<U>& that) : _value(that.getval()) {}
  14.  
  15.    // I'm sure this it can be done without this being public also;
  16.    T getval() const { return _value ; }; 
  17.  
  18.    foo(const T& that) : _value(that) {}
  19.  
  20.    friend foo& operator +=(foo &lhs,const foo &rhs)
  21.       {
  22.      lhs._value+=rhs._value;
  23.      return lhs;
  24.       };   
  25.    friend std::ostream& operator<<(std::ostream& out, const foo& me){
  26.       return out <<me._value;
  27.    }
  28. };
  29.  
  30. template <typename T, typename U>
  31. const foo<T> operator +(foo<T> &lhs,const foo<U> &rhs) 
  32.       {
  33.      foo<T> result(lhs._value+rhs._value); 
  34.      return result;
  35.       }
  36. template <typename T>
  37.    const foo<T> operator +(foo<T> &lhs,const T &rhsval) 
  38.       {
  39.      foo<T> result(lhs._value+rhsval); 
  40.      return result;
  41.       }
  42. template <typename T>
  43.    const foo<T> operator +(const T &lhsval,foo<T> &rhs) 
  44.       {
  45.      foo<T> result(lhsval+rhs._value); 
  46.      return result;
  47.       }
  48.  
  49.  
  50. int main(){
  51.    foo< int > f, g;
  52.    foo< double > dd;
  53.    cout <<f<<endl;
  54.    f = f + g;
  55.    cout <<f<<endl;
  56.    f += 3 ;
  57.    cout <<f<<endl;
  58.    f = f + 5;
  59.    cout <<f<<endl;
  60.    f = 7 + f; 
  61.    cout <<f<<endl;      
  62.    dd=dd+f;
  63.    cout <<dd<<endl;      
  64.    dd=f+dd;
  65.    cout <<dd<<endl;      
  66.    dd=dd+7.3;
  67.    cout <<dd<<endl;             
  68. }
  69.  
Success #stdin #stdout 0s 3340KB
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37.3
https://ideone.com/0hMp83
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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