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  1. #include <type_traits>
  2. #include <memory>
  3. #include <iostream>
  4.  
  5. namespace detail
  6. {
  7.     template <typename T>
  8.     struct wrapper
  9.     {
  10.         virtual ~wrapper() {}
  11.         virtual T const * get() const = 0;
  12.         virtual T * get() = 0;
  13.     };
  14.  
  15.     template <typename T, typename F>
  16.     struct storage
  17.         : wrapper<T>
  18.     {
  19.         storage(F f)
  20.         {
  21.             p_ = f();
  22.         }
  23.  
  24.         T const * get() const { return p_.get(); }
  25.         T * get() { return p_.get(); }
  26.  
  27.         private:
  28.             typename std::result_of<F()>::type p_;
  29.     };
  30. }
  31.  
  32. template <typename T>
  33. class some_class
  34. {
  35.     public:
  36.         template <typename F>
  37.         void store(F f)
  38.         {
  39.             storage_.reset(new detail::storage<T, F>(f));
  40.         }
  41.  
  42.         T const * get() const { return storage_->get(); }
  43.         T * get() { return storage_->get(); }
  44.  
  45.     private:
  46.         std::unique_ptr<detail::wrapper<T>> storage_;
  47. };
  48.  
  49. struct foo
  50. {
  51.     void bar() const { std::cout << "hello" << '\n'; }
  52. };
  53.  
  54. int main()
  55. {
  56.     some_class<foo> a;
  57.     a.store([]() { return std::unique_ptr<foo>(new foo()); });
  58.     a.get()->bar();
  59.     a.store([]() { return std::unique_ptr<
  60.         foo, std::default_delete<foo[]>
  61.     >(new foo[1], std::default_delete<foo[]>()); });
  62.     a.get()[0].bar();
  63.  
  64.     return 0;
  65. }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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hello
hello
https://ideone.com/C5WMgj
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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