Re: address of virtual member function passed as template argument

25 Mar 2007 13:44:34 -0700
On 19 Mrz., 20:38, "Ben Voigt" <r...@nospam.nospam> wrote:

"Igor Tandetnik" <> wrote in message


Ben Voigt <r...@nospam.nospam> wrote:

"Igor Tandetnik" <> wrote in message
news:etcVaEkaHHA.2436@TK2MSFTNGP06.phx.gbl... wrote:

It's a pitty that there are no std c++ properties.

You can mimic them to some extent. Here's a rough draft:

The OP was trying to use boost::property which does everything you

I didn't know there was such a thing. I can't seem to find it on

Hmm, the OP claimed there was. A quick google search turns up:

boost-sandbox is described as a place to propose boost modules. Perhaps it
got rejected from main boost.

With best wishes,
   Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

Yes, that's the library i was talking about. Sorry for not posting a
Thank you all for your great ideas for good property solution.

The proxy-Version from Ben Voigt compiles very well, but it is a lot
of work to write a wrapper function for every function.
The Observer-Version from Igor Tandetnik is also very interesting,
but what about class-inheritance ? i think you will run into problems
with that.
Another problem is that the value is stored within the property which
is a restriction in a way.

You should also be able to write properties which don't store values
but only call C-API functions or so.

I think it would be best if we could specify the get/set - functions
is a separate struct.
Like this:

class Car
struct SpeedProp
int get() {}
void set(int) {}

So here is my solution:
// main.cpp - draft for properties

#include <iostream>

template<class T>
class IPropertyImplementation
    virtual ~IPropertyImplementation() {}

    virtual void set(const T& value) = 0;
    virtual T get() const = 0;

template<class T>
class property
    IPropertyImplementation<T>* prop;

    property(IPropertyImplementation<T>* prop)
        : prop(prop)

        if(prop) // i know that this is not safe, but this is only a draft
            delete prop;

    property<T>& operator=(const T& value)
        return *this;

    operator T()
        return prop->get();

        // more operators etc.

class Car
    int speed;

    struct SpeedProperty : public IPropertyImplementation<int>
        Car* base; // pointer to car object
        SpeedProperty(Car* base) : base(base) {}

        void set(const int& value) { base->speed = value; }
        int get() const { return base->speed; }
    friend struct SpeedProperty; // needed?

    property<int> Speed;

        : Speed(new SpeedProperty(this))

int main(int argc, char* argv[])
    Car c;
    c.Speed = 2007;
    std::cout << c.Speed << std::endl; // -> 2007
    return 0;

What do you guys think about it? Any ideas for improvements or other

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