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  1. #include <algorithm>
  2. #include <iostream>
  3. #include <vector>
  4. #include <memory>
  5.  
  6. struct entity {  //Simple struct of data.
  7.      bool alive;
  8.      float data;
  9. };
  10.  
  11. class manager {
  12.     std::vector<std::shared_ptr<entity>> vec;  
  13. public:
  14.  
  15.     //Reserves initial_amount of entities
  16.     explicit manager(size_t initial_amount) { vec.reserve(initial_amount); }
  17.  
  18.     std::weak_ptr<entity> create(float f) {
  19.         vec.push_back(std::make_unique<entity>(entity{true, f}));
  20.         return vec.back();
  21.     }
  22.  
  23.     void refresh() {
  24.         vec.erase(std::remove_if(vec.begin(), vec.end(),
  25.                                  [](const auto& ent) {return !ent->alive;}),
  26.                   vec.end());
  27.     }
  28.  
  29.     void grow(size_t n) { vec.reserve(n); }
  30.  
  31.     void print() const { //Prints all alive entities.
  32.         for (const auto& ent : vec)
  33.             std::cout << ent->data << " ";
  34.         std::cout << std::endl;
  35.     }
  36. };
  37.  
  38. int main() {
  39.     manager c(10);
  40.     auto d1 = c.create(5.5);
  41.     auto d2 = c.create(10.5);
  42.     auto d3 = c.create(7.5);
  43.  
  44.     // Correct behavior
  45.     if (auto e = d1.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 5.5
  46.     if (auto e = d2.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 10.5
  47.     if (auto e = d3.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 7.5
  48.     std::cout << std::endl;
  49.  
  50.     if (auto e = d2.lock()) e->alive = false;        // "Kill" the entity
  51.     c.refresh();             // removes all dead entities.
  52.  
  53.     if (auto e = d1.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 5.5
  54.     if (auto e = d2.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // Die
  55.     if (auto e = d3.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 10.5
  56.     std::cout << std::endl;
  57.  
  58.     c.print();               // Correct behavior, prints only alive entities.
  59.     std::cout << std::endl;
  60.  
  61.     if (auto e = d3.lock()) e->data = 6.5; // Trying to change the value of d3,
  62.                                            // which should still be alive.
  63.     c.print();
  64.     std::cout << std::endl;
  65.  
  66.     c.grow(10000);
  67.  
  68.     if (auto e = d1.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 5.5
  69.     if (auto e = d2.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // Die
  70.     if (auto e = d3.lock()) std::cout << e->data << std::endl; else std::cout << "Die\n"; // 6.5
  71. }
  72.  
Success #stdin #stdout 0s 3476KB
comments (?)
stdin
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Standard input is empty
stdout
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5.5
10.5
7.5

5.5
Die
7.5

5.5 7.5 

5.5 6.5 

5.5
Die
6.5
https://ideone.com/SbZkN4
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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