property in C++

From:
"theambient" <tiabaldu@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 27 Jul 2010 15:51:13 +0000 (UTC)
Message-ID:
<i2mv9h$cr1$1@speranza.aioe.org>
hi,

I want make property
(http://en.wikipedia.org/wiki/Property_(programming)) in C++.

In the wiki article explained how to make property in C++ using
template mechanism

this looks like

========================================================================
========================================================================
template <typename T> class property {
        T value;
    public:
        T & operator = (const T &i) {
            ::std::cout << i << ::std::endl;
            return value = i;
        }
        // This template class member function template serves the
purpose to make
        // typing more strict. Assignment to this is only possible with
exact identical
        // types.
        template <typename T2> T2 & operator = (const T2 &i) {
            ::std::cout << "T2: " << i << ::std::endl;
            T2 &guard = value;
            throw guard; // Never reached.
        }
        operator T const & () const {
            return value;
        }
};
========================================================================
========================================================================

everything is clear (except never reached throw, aprreciate if anybody
explain it to me)

i wish to extend functionality of this property to get addaptable
setting and getting (mechanism) passed to property as template
arguments.

I see it as pointers to member functions.

so i've implemented something:

========================================================================
========================================================================

#include <iostream>

template <typename T, typename C >
class property {

    typedef void(C::*PMANIP)( T & i ) ;

    mutable T value;

    PMANIP _set;
    PMANIP _get;
    C & _c;
public:
    property( C & c, PMANIP set, PMANIP get ): _set(set), _get(get),
_c(c){}

    T & operator = (const T &i) {
        value = i;
        (_c.*_set)(value);
        return value;
    }

    operator T const & () const {
        (_c.*_get)(value);
        return value;
    }
};

struct Foo {

    void set( int &i ){ std::cout << "setting " << i << std::endl; }
    void get( int &i ){ std::cout << "getting " << i << std::endl; }

    property<int, Foo> val;
    Foo():val( *this, &Foo::set, &Foo::get ){}
};

int main(int argc, char** argv )
{
    Foo foo;
    std::cout << "foo.val = " << foo.val << std::endl;
    foo.val = 10;
    std::cout << "foo.val = " << foo.val << std::endl;

    return 0;
}
========================================================================
========================================================================

really nasty cause we need initialize property in !!!EACH!!!
constructor with class instance reference (*this) and pointers to
setter and getter functions.

As far as i understand pointers to setter and getter can be passed as
template parameters.

How to do it?

I can't make typedef in template parameters list to write something
like
template <typename T, typename C, PMANIP Setter, PMANIP Getter>

and anyway i'll need to initialize property with class instance
reference.

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