Revisiting how to implement __property in ansi c++

[DaleC]

I have the same problem as discussed at

http://bytes.com/topic/c/answers/133424-how-implement-__property-ansi-c

The best solution there looks like this one, but I cannot get it to compile - see embedded comments. Any advice much appreciated.

template <typename T, typename C>
 class Property
 {
 typedef T (C::*Get)() const;
 typedef void (C::*Set)(T);
 Get GetFunc_;
 Set SetFunc_;
 C & Class_;
 public:
 Property(Get GetFunc, Set SetFunc, C &Class)
 : GetFunc_(GetFunc), SetFunc_(SetFunc), Class_(Class) {}

 operator T () const
 {
 return (Class_.*GetFunc_)();
 }

 Property<T, C>& operator=(T val)
 {
 (Class_.*SetFunc_)(val);
 return *this;
 }
 };

 class TMyClass
 {
 int FMyVariable;
 public:
 Property<int, TMyClass> MyVariable;
 // fails at the line below in an MFC compile using VS2013
 // wants argument lists, so I changed to
 // TMyClass() : MyVariable(GetMyVariable(), SetMyVariable(int), *this)
 // but no good.
 TMyClass() : MyVariable(GetMyVariable, SetMyVariable, *this)
 {
 }
 int GetMyVariable() const
 {
 return FMyVariable;
 }
 void SetMyVariable(int Value)
 {
 FMyVariable = Value;
 }
 };

[weaknessforcats]

This is a problem:

TMyClass() : MyVariable([B]GetMyVariable[/B], [B]SetMyVariable[/B], *this)
 {
 }
 int GetMyVariable() const
 {
 return FMyVariable;
 }
 void SetMyVariable(int Value)
 { 
 FMyVariable = Value;
 }

Here two function pointers are being used before the compiler has seen the functions.

Often the trick to templates is to code the classes without using templates until it compiles and links. Then convert the class declarations to templates.

[DaleC]

Hi weakness,

Thanks for the suggestion. Some further googling found a solution. If I change TMyClass constructor to

<code>
class TMyClass
{
int FMyVariable;
public:
Property<int, TMyClass3> MyVariable;
TMyClass() : FMyVariable(0), MyVariable(&TMy Class::GetMyVar iable, &TMyClass::SetM yVariable, *this) {}
int GetMyVariable() const
{
return FMyVariable;
}
void SetMyVariable(i nt Value)
{
FMyVariable = Value;
}
};
</code>

then it compiles and works.

[weaknessforcats]

OK.

However, in looking at your code it looks like you have a Visitor design pattern in disguise.

Read this: http://bytes.com/topic/c/insights/67...tterns-visitor

Let me know what you think.