C++ Linkable Properties - c++

Question

I'm trying to create a relatively type safe(but dynamic) and efficient concept called "Linkable Properties". A linkable property is similar to C#'s ability to bind properties and such and similar to the signal/slot model.
A linkable property is a type that can link itself to the values of other types. When any value changes all values are updated. This is useful when you need to keep several properties/values updated simultaneously. Once you setup a link everything is taken care of for you.
Can link from any type to any other type (in theory, this is the issue)
Links use a linked list rather than a list. This is more efficient both memory and speed and the real benefit of using this approach.
Converters are used to convert the values from one type to another(from 1, required, also an issue)
Can act like a getter and setter.
The issues I'm struggling with is writing the ability to link and convert to any type. The following code works with minor changes(convert the templated Chain function to a non-templated version and Change Chain<F> to Chain in the SetLink function). The problem is, the links are not correctly called.
This class almost works(it does compile and run but does not work as expected. Without the changes above the binding function never calls. It is only test code and not properly coded(please don't comment about using the static counter, it's just a temporary fix). The Chain and Link elements are the crucial aspect.
Chain is simply suppose to convert and update the value of the property then pass it along(or possibly the original value) to the next property. This continues until one reaches back to the original property in which case it will terminate.
#include <iostream>
#include <string>
#include <boost/bind.hpp>
#include <boost/function.hpp>
using namespace std;
static int iLCount = 1;
template <typename T>
class LinkableProperty
{
public:
std::string Name;
boost::function<void(T)> Link;
T Value;
template<typename F>
void Chain(F val)
{
Value = val;
std::cout << this->Name << " - " << this << ", " << &Link << ", " << val << " ! " << this->Value << " - " << "\n";
if (--iLCount < 0) return;
if (!Link.empty()) Link(Value);
}
LinkableProperty() { Link = NULL; Value = T(); Name = "Level " + std::to_string(iLCount++); };
void operator =(T value) { Value = value; }
template<typename F> void SetLink(LinkableProperty<F> &p)
{
Link = boost::bind(&LinkableProperty<F>::template Chain<F>, &p, _1);
}
void operator ()()
{
if (!Link.empty()) Link(Value);
}
};
int main()
{
LinkableProperty<unsigned short> L1;
LinkableProperty<double> L2;
L2.SetLink(L1);
L1.SetLink(L2);
L1 = 1;
L2 = 1.1;
L1();
cout << "----------\n" << L1.Value << ", " << L2.Value << endl;
getchar();
return 0;
}

Answer 1

The problem most likely stems from here:
template<typename F> void SetLink(LinkableProperty<F> p)
You are passing in a copy of the original property. Change this to accept a reference (or pointer), and you may have better luck. For example:
template<typename F>
void SetLink(LinkableProperty<F>* p)
{
Link = boost::bind(&LinkableProperty<F>::template Chain<F>, p, _1);
}
Should work as expected...
EDIT: Updated to show how to preserve the type across the conversion:
template <typename FT, typename TT>
TT convert(FT v)
{
return v; // default implicit conversion
}
template<>
double convert(unsigned short v)
{
std::cout << "us->d" << std::endl;
return static_cast<double>(v);
}
template<>
unsigned short convert(double v)
{
std::cout << "d->us" << std::endl;
return static_cast<unsigned short>(v);
}
static int iLCount = 1;
template <typename T>
class LinkableProperty
{
template <typename U>
struct _vref
{
typedef U vt;
_vref(vt& v) : _ref(v) {}
U& _ref;
};
public:
std::string Name;
boost::function<void(_vref<T>)> Link;
T Value;
template<typename F>
void Chain(F const& val)
{
Value = convert<typename F::vt, T>(val._ref);
std::cout << this->Name << " - " << this << ", " << &Link << ", " << val._ref << " ! " << this->Value << " - " << "\n";
if (--iLCount < 0) return;
if (!Link.empty()) Link(Value);
}
LinkableProperty() { Link = NULL; Value = T(); Name = "Level " + std::to_string(iLCount++); };
void operator =(T value) { Value = value; }
template<typename F>
void SetLink(LinkableProperty<F>* p)
{
Link = boost::bind(&LinkableProperty<F>::template Chain<_vref<T>>, p, _1);
}
void operator ()()
{
if (!Link.empty()) Link(_vref<T>(Value));
}
};
int main()
{
LinkableProperty<unsigned short> L1;
LinkableProperty<double> L2;
L2.SetLink(&L1);
L1.SetLink(&L2);
L1 = 1;
L2 = 1.1;
L1();
cout << "----------\n" << L1.Value << ", " << L2.Value << endl;
getchar();
return 0;
}
NOTE: There is some link bug which means that the updates trigger more times than necessary - you should check that...