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  1. namespace bicycle
  2. {
  3.     template<typename Result,typename ...Args>
  4.     struct abstract_function
  5.     {
  6.         virtual Result operator()(Args... args)=0;
  7.         virtual abstract_function *clone() const =0;
  8.         virtual ~abstract_function() = default;
  9.     };
  10.  
  11.     template<typename Func,typename Result,typename ...Args>
  12.     class concrete_function: public abstract_function<Result,Args...>
  13.     {
  14.         Func f;
  15.     public:
  16.         concrete_function(const Func &x)
  17.             : f(x)
  18.         {}
  19.         Result operator()(Args... args) override
  20.         {
  21.             return f(args...);
  22.         }
  23.         concrete_function *clone() const override
  24.         {
  25.             return new concrete_function{f};
  26.         }
  27.     };
  28.  
  29.     template<typename Func>
  30.     struct func_filter
  31.     {
  32.         typedef Func type;
  33.     };
  34.     template<typename Result,typename ...Args>
  35.     struct func_filter<Result(Args...)>
  36.     {
  37.         typedef Result (*type)(Args...);
  38.     };
  39.  
  40.     template<typename signature>
  41.     class function;
  42.  
  43.     template<typename Result,typename ...Args>
  44.     class function<Result(Args...)>
  45.     {
  46.         abstract_function<Result,Args...> *f;
  47.     public:
  48.         function()
  49.             : f(nullptr)
  50.         {}
  51.         template<typename Func> function(const Func &x)
  52.             : f(new concrete_function<typename func_filter<Func>::type,Result,Args...>(x))
  53.         {}
  54.         function(const function &rhs)
  55.             : f(rhs.f ? rhs.f->clone() : nullptr)
  56.         {}
  57.         function &operator=(const function &rhs)
  58.         {
  59.             if( (&rhs != this ) && (rhs.f) )
  60.             {
  61.                 auto *temp = rhs.f->clone();
  62.                 delete f;
  63.                 f = temp;
  64.             }
  65.             return *this;
  66.         }
  67.         template<typename Func> function &operator=(const Func &x)
  68.         {
  69.             auto *temp = new concrete_function<typename func_filter<Func>::type,Result,Args...>(x);
  70.             delete f;
  71.             f = temp;
  72.             return *this;
  73.         }
  74.         Result operator()(Args... args)
  75.         {
  76.             if(f)
  77.                 return (*f)(args...);
  78.             else
  79.                 return Result{};
  80.         }
  81.         ~function()
  82.         {
  83.             delete f;
  84.         }
  85.     };
  86. }
  87.  
  88. // ___________________[ Example of usage ]___________________ //
  89.  
  90. int func1(double)
  91. {
  92.     return 1;
  93. }
  94. struct Functor2
  95. {
  96.     int operator()(double)
  97.     {
  98.         return 2;
  99.     }
  100. };
  101.  
  102. double func3(bool,int)
  103. {
  104.     return 3.0;
  105. }
  106. struct Functor4
  107. {
  108.     double operator()(bool,int)
  109.     {
  110.         return 4.0;
  111.     }
  112. };
  113.  
  114. int main()
  115. {
  116.     int res = 10;
  117.     {
  118.         bicycle::function<int(double)> f{func1};
  119.  
  120.         res -= f(1.0);
  121.         f = Functor2{};
  122.         res -= f(2.0);
  123.     }
  124.     {
  125.         bicycle::function<double(bool,int)> f1;
  126.         f1 = func3;
  127.  
  128.         bicycle::function<double(bool,int)> f2{f1};
  129.         res -= f2(true,1);
  130.  
  131.         f1 = Functor4{};
  132.         f2 = f1;
  133.         res -= f2(false,2);
  134.     }
  135.     return res;
  136. }
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https://ideone.com/zY2p2q
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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