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2012-02-23T11:43:11.657
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2012-02-23T11:43:11.657
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Creating a property helper class that must be instanciated as a member of the class you want to add property on is a bad idea, since you'll have the cost of the property members for all the instances of this class. A solution that offers a "property" mechanism close to what other languages offer can be made available in C++ using something like what I describe later. The only limitation being that you access the property using instance.property(); // to get and instance.property() = 42; // to set <pre><code>#include <iostream> #include <string> using namespace std; // ------------------------------------------------------------------ #define PROPERTY_GET_SET(CLASS, NAME, TYPE) GetSetProperty<CLASS, TYPE> NAME() { return GetSetProperty<CLASS, TYPE>(this, &CLASS::get_##NAME, &CLASS::set_##NAME); } #define PROPERTY_GET(CLASS, NAME, TYPE) GetProperty<CLASS, TYPE> NAME() { return GetProperty<CLASS, TYPE>(this, &CLASS::get_##NAME); } #define PROPERTY_SET(CLASS, NAME, TYPE) SetProperty<CLASS, TYPE> NAME() { return SetProperty<CLASS, TYPE>(this, &CLASS::set_##NAME); } template <typename CLASS, typename TYPE> struct GetSetProperty { typedef TYPE (CLASS::*Getter_t)() const; typedef void (CLASS::*Setter_t)(TYPE); GetSetProperty(CLASS* instance, Getter_t getter, Setter_t setter) : m_instance(instance), m_getter(getter), m_setter(setter) {} operator TYPE() const { return (this->m_instance->*this->m_getter)(); } GetSetProperty<CLASS, TYPE>& operator=(TYPE value) { (this->m_instance->*this->m_setter)(value); return *this; } CLASS* const m_instance; const Getter_t m_getter; const Setter_t m_setter; }; template <typename CLASS, typename TYPE> struct GetProperty { typedef TYPE (CLASS::*Getter_t)() const; GetProperty(CLASS* instance, Getter_t getter) : m_instance(instance), m_getter(getter) {} operator TYPE() const { return (this->m_instance->*this->m_getter)(); } CLASS* const m_instance; const Getter_t m_getter; }; template <typename CLASS, typename TYPE> struct SetProperty { typedef void (CLASS::*Setter_t)(TYPE); SetProperty(CLASS* instance, Setter_t setter) : m_instance(instance), m_setter(setter) {} SetProperty<CLASS, TYPE>& operator=(TYPE value) { (this->m_instance->*this->m_setter)(value); return *this; } CLASS* const m_instance; const Setter_t m_setter; }; template <typename CLASS, typename TYPE> ostream& operator<<(ostream& ostr, const GetSetProperty<CLASS, TYPE>& p) { ostr << (p.m_instance->*p.m_getter)(); return ostr; } template <typename CLASS, typename TYPE> ostream& operator<<(ostream& ostr, const GetProperty<CLASS, TYPE>& p) { ostr << (p.m_instance->*p.m_getter)(); return ostr; } // ------------------------------------------------------------------ class Dummy { public: Dummy() : m_value1(42) {} PROPERTY_GET_SET(Dummy, Value1, int); PROPERTY_GET_SET(Dummy, Value2, const string&); protected: virtual int get_Value1() const { return this->m_value1; } virtual void set_Value1(int value) { this->m_value1 = value; } virtual const string& get_Value2() const { return this->m_value2; } virtual void set_Value2(const string& value) { this->m_value2 = value; } private: int m_value1; string m_value2; }; int main(int argc, char* argv[]) { Dummy d; cout << d.Value1() << endl; d.Value1() = 3; cout << d.Value1() << endl; cout << d.Value2() << endl; d.Value2() = "test"; cout << d.Value2() << endl; return 0; } // ------------------------------------------------------------------ </code></pre>
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1. POc++ derive pure abstract w/ nested struct
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1. USrlods
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1. COThis is a nice, valid answer. I especially like the nice macro examples. Since Macro programming is the one thing I struggle with most, this was helpful. It *may* or may not be the solution I go with, but I'm flagging it as an answer for future readers to find a nice solid answer.
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