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  1. #include <alloca.h>
  2. #include <iostream>
  3. #include <vector>
  4.  
  5. struct Base
  6. {
  7.     virtual ~Base() { }
  8.     virtual int to_int() const = 0;
  9. };
  10.  
  11. struct Integer : Base
  12. {
  13.     Integer(int n) : n_(n) { }
  14.     int to_int() const { return n_; }
  15.     int n_;
  16. };
  17.  
  18. struct Double : Base
  19. {
  20.     Double(double n) : n_(n) { }
  21.     int to_int() const { return -n_; }
  22.     double n_;
  23. };
  24.  
  25. inline Base* factory(double d) __attribute__((always_inline));
  26.  
  27. inline Base* factory(double d)
  28. {
  29.     if ((double)(int)d != d)
  30.         return new (alloca(sizeof(Double))) Double(d);
  31.     else
  32.         return new (alloca(sizeof(Integer))) Integer(d);
  33. }
  34.  
  35. int main()
  36. {
  37.     std::vector<Base*> numbers;
  38.     numbers.push_back(factory(29.3));
  39.     numbers.push_back(factory(29));
  40.     numbers.push_back(factory(7.1));
  41.     numbers.push_back(factory(2));
  42.     numbers.push_back(factory(231.0));
  43.     std::cerr << "iterating...\n";
  44.     for (std::vector<Base*>::const_iterator i = numbers.begin();
  45.          i != numbers.end(); ++i)
  46.     {
  47.         std::cout << *i << ' ' << (*i)->to_int() << '\n';
  48.         (*i)->~Base();   // optionally / Undefined Behaviour iff the
  49.                          // program depends on side effects of destructor
  50.     }
  51. }
  52.  
Success #stdin #stdout #stderr 0s 3432KB
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stdin
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Standard input is empty
stdout
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0xbfbd5d90 -29
0xbfbd5d70 29
0xbfbd5d50 -7
0xbfbd5d30 2
0xbfbd5d10 231
stderr
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iterating...
https://ideone.com/XIBes5
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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