Recently I'd touched an article about properties in python. They were implemented using special function property and looked very elegant:
class A(object):
def __init__(self):
self._x = None
def get_x(self):
return self._x
def set_x(self, x):
self._x = x
x = property(get_x, set_x)
obj = A()
obj.x = 6 # set
print obj.x # get
We don't have such option in c++. But it's quite simple to create one. Some implementation I saw were ugly indeed. They used a lot of code and wanted to call some routines in constructor.
My version of property in c++:#include <iostream>
template<typename T,
T(*s)(T &, const T &),
T(*g)(T &)>
class property
{
public:
T operator =(const T &nt)
{
return s(t, nt);
}
operator T()
{
return g(t);
}
protected:
T t;
};
class A
{
public:
static int setter(int &i, const int &ni)
{
cout << "S" << endl;
i = ni;
return i;
}
static int getter(int &i)
{
cout << "G" << endl;
return i;
}
property<int, setter, getter> p;
};
int main(int argc, char **argv)
{
A a;
a.p = 6;
std::cout << a.p;
return 0;
}You have to define 2 static class methods(or just functions, doesn't matter) for setter and getter of the property.
The modified version of class property may have default setter and getter:template<typename T>
T setter(T &i, const T &ni)
{
i = ni;
return i;
}
template<typename T>
T getter(T &i)
{
return i;
}
template<typename T,
T(*s)(T &, const T &) = setter<T>,
T(*g)(T &) = getter<T> >
class property
{
public:
T operator =(const T &nt)
{
return s(t, nt);
}
operator T()
{
return g(t);
}
protected:
T t;
};Now you can customize only one of them:int getter(int &i)
{
cout << "G" << endl;
return i;
}
class A
{
public:
A(int a)
{
p = a;
}
property<int, setter<int>, getter> p;
};
