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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. class Foo {
  5.     enum OpState {
  6.     	None ,
  7.     	PlusState ,
  8.     	NotState ,
  9.     };
  10.  
  11. public:
  12.     friend Foo& operator+(Foo& lhs, const Foo& rhs) {
  13. 		cout << "operator+(Foo& lhs, const Foo& rhs)" << endl;
  14. 		if(lhs.opState == NotState) {
  15. 		    return lhs.operatorexclamativeplus(rhs);
  16. 		}
  17. 		return lhs;
  18. 	}
  19.  
  20.    Foo& operator+() {
  21.    	   cout << "operator+()" << endl;
  22.        opState = PlusState;
  23.        return *this;
  24.    }
  25.    Foo& operator!() {
  26.    	   cout << "operator!()" << endl;
  27.        switch(opState) {
  28.        case PlusState:
  29.            operatorexclamativeplus();
  30.            opState = None;
  31.            break;       
  32.        default:
  33.            opState = NotState;
  34.            break;       
  35.        }
  36.        return *this;
  37.    }
  38.  
  39. private:
  40.     void operatorexclamativeplus() {
  41.    	   cout << "operatorexclamativeplus()" << endl;
  42.     }
  43.     Foo& operatorexclamativeplus(const Foo& rhs) {
  44.    	   cout << "operatorexclamativeplus(const Foo& rhs)" << endl;
  45.    	   return *this;
  46.     }
  47.  
  48.     OpState opState;
  49. };
  50.  
  51.  
  52. int main() {
  53. 	Foo x;
  54. 	Foo y;
  55. 	!+x;
  56. 	Foo z = y !+ x;
  57. 	return 0;
  58. }
Compilation error #stdin compilation error #stdout 0s 3340KB
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stdin
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Standard input is empty
compilation info 
prog.cpp: In function ‘int main()’:
prog.cpp:56:12: error: expected ‘,’ or ‘;’ before ‘!’ token
  Foo z = y !+ x;
            ^
stdout
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Standard output is empty
https://ideone.com/YPRysQ
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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