fork download
copy 
  1. #include <iostream>
  2. #include <cassert>
  3.  
  4. namespace functional_vector {
  5.  
  6.   template<typename T>
  7.   class optional_t {
  8.   public:
  9.     optional_t(): m_value{nullptr}{}
  10.  
  11.     template<typename ...Args>
  12.     optional_t(Args&&...args): m_value{ new T{ std::forward<Args>(args)... }}{}
  13.     // optional_t(T const &val): m_value{ new T{val} }{}
  14.     ~optional_t(){ reset(); }
  15.  
  16.     bool has_value(){ return m_value != nullptr; }
  17.  
  18.     T* operator->(){ 
  19.       return m_value;
  20.     }
  21.  
  22.     T& operator*(){
  23.       assert(m_value);
  24.       return *m_value;
  25.     }
  26.  
  27.     T& value(){
  28.       assert(m_value);
  29.       return *m_value;
  30.     }
  31.  
  32.     T const & value() const {
  33.       assert(m_value);
  34.       return *m_value;
  35.     }
  36.  
  37.     optional_t<T>& operator=( T const & value ){
  38.       assert(m_value);
  39.       *m_value = value;
  40.       return *this;
  41.     }
  42.  
  43.     template<typename ...Args>
  44.     T& emplace(Args && ...args){
  45.       reset();
  46.       m_value = new T( std::forward<Args>(args)... );
  47.       return *m_value;
  48.     }
  49.  
  50.   private:
  51.     void reset(){
  52.       if(m_value){
  53.         delete m_value;
  54.         m_value = nullptr;
  55.       }
  56.     }
  57.  
  58.     T* m_value;
  59.   };  
  60. }
  61.  
  62. struct foo_t {
  63.   int a{};
  64. };
  65.  
  66. template<typename T>
  67. using opt_value_t = functional_vector::optional_t<T>;
  68. using opt_string_t = opt_value_t<std::string>;
  69.  
  70.  
  71. int main(int argc, char **argv)
  72. {
  73. 	opt_string_t opt_string{};
  74.   std::cout << std::boolalpha << opt_string.has_value() << std::endl;
  75.  
  76.   auto& str = opt_string.emplace(10, 'a');
  77.  
  78.   std::cout << opt_string.has_value() << std::endl << std::noboolalpha;
  79.  
  80.   std::cout << opt_string.value() << " " << *opt_string 
  81.     << " " << str << std::endl << std::endl;
  82.  
  83.   opt_value_t<foo_t> foo{10};
  84.   std::cout << foo->a << std::endl; 
  85. 	return 0;
  86. }
  87.  
  88.  
Success #stdin #stdout 0.01s 5508KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
false
true
aaaaaaaaaa aaaaaaaaaa aaaaaaaaaa

10
https://ideone.com/e2NTu9
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!