Property (programming)

#include <iostream>

template <typename T> class property {
        T value;
    public:
        T & operator = (const T &i) {
            return value = i;
        }
        // This template class member function template serves the purpose to make
        // typing more strict. Assignment to this is only possible with exact identical types.
        // The reason why it will cause an error is temporary variable created while implicit type conversion in reference initialization.
        template <typename T2> T2 & operator = (const T2 &i) {
            T2 &guard = value;
            throw guard; // Never reached.
        }

        // Implicit conversion back to T. 
        operator T const & () const {
            return value;
        }
};

struct Foo {
    // Properties using unnamed classes.
    class {
            int value;
        public:
            int & operator = (const int &i) { return value = i; }
            operator int () const { return value; }
    } alpha;

    class {
            float value;
        public:
            float & operator = (const float &f) { return value = f; }
            operator float () const { return value; }
    } bravo;
};

struct Bar {
    // Using the property<>-template.
    property <bool> alpha;
    property <unsigned int> bravo;
};

int main () {
    Foo foo;
    foo.alpha = 5;
    foo.bravo = 5.132f;

    Bar bar;
    bar.alpha = true;
    bar.bravo = true; // This line will yield a compile time error
                      // due to the guard template member function.
    ::std::cout << foo.alpha << ", "
                << foo.bravo << ", "
                << bar.alpha << ", "
                << bar.bravo
                << ::std::endl;
    return 0;
}

// declspec_property.cpp
struct S
{
   int i;
   void putprop(int j)
   { 
      i = j;
   }

   int getprop()
   {
      return i;
   }

   __declspec(property(get = getprop, put = putprop)) int the_prop;
};

int main()
{
   S s;
   s.the_prop = 5;
   return s.the_prop;
}