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  1. #include <functional>
  2. #include <iostream>
  3. #include <cassert>
  4.  
  5. int    foo(double d) { return d; }
  6.  
  7. double bar(double d) { return 2*d; }
  8.  
  9. struct Result {
  10. 	union {
  11. 		int    i_res;
  12. 		double d_res;
  13. 	};
  14. 	enum { IS_INT, IS_DOUBLE } u_tag;
  15.  
  16. 	Result(Result const&) = default;
  17. 	Result(int i)  : i_res{i}, u_tag{IS_INT} {}
  18. 	Result(double d) : d_res{d}, u_tag{IS_DOUBLE} {}
  19.  
  20. 	Result& operator=(Result const&) = default;
  21. 	auto& operator=(int i)
  22. 	{ i_res = i; u_tag = IS_INT;    return *this; }
  23. 	auto& operator=(double d)
  24. 	{ d_res = d; u_tag = IS_DOUBLE; return *this; }
  25. };
  26.  
  27. int main() {
  28. 	std::function<Result(double)> cb;
  29.  
  30. 	cb = foo;
  31. 	auto r = cb(1.0);
  32. 	assert(r.u_tag == Result::IS_INT);
  33. 	std::cout << r.i_res << '\n';
  34.  
  35. 	cb = bar;
  36. 	r = cb(2.0);
  37. 	assert(r.u_tag == Result::IS_DOUBLE); 
  38. 	std::cout << r.d_res << '\n';
  39.  
  40. 	return 0;
  41. }
Success #stdin #stdout 0s 16064KB
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https://ideone.com/gxAA98
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
secret

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