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  1. #include <iostream>
  2. #include <type_traits>
  3. using namespace std;
  4.  
  5. struct alfa {};
  6.  
  7. struct foo { foo() { cout << "foo(void)" << endl; }};
  8.  
  9. struct bar { explicit bar(alfa&) { cout << "bar(alfa&)" << endl; } };
  10.  
  11. template<class T> struct with_allocator
  12. {
  13. 	struct unspecified_type;
  14.  
  15. 	T var;
  16. 	T& operator*() { return var; }
  17. 	T const& operator*() const { return var; }
  18.  
  19. 	template<class A>
  20. 	explicit with_allocator(A& a, typename enable_if< is_constructible<T,A&>::value, unspecified_type* >::type _ = nullptr)
  21. 	: var(a)
  22. 	{ cout << "with allocator" << endl; }
  23.  
  24. 	template<class A>
  25. 	explicit with_allocator(A& a, typename enable_if<!is_constructible<T,A&>::value, unspecified_type* >::type _ = nullptr)
  26. 	{ cout << "without allocator" << endl; }
  27. };
  28.  
  29. void run(foo&, bar&) { cout << "run(foo,bar)" << endl; }
  30.  
  31. int main() {
  32. 	// your code goes here
  33. 	alfa a;
  34.  
  35. 	with_allocator<foo> f (a);
  36. 	with_allocator<bar> b (a);
  37.  
  38. 	run(*f, *b);
  39. 	return 0;
  40. }
  41.  
Success #stdin #stdout 0s 3296KB
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stdin
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Standard input is empty
stdout
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foo(void)
without allocator
bar(alfa&)
with allocator
run(foo,bar)
https://ideone.com/8fwXl9
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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