Re: [Boost-users] Is it possible to makeaclass assignablewithrefmembers

From: John Femiani (JOHN.FEMIANI_at_[hidden])
Date: 2008-05-21 06:16:03

Max wrote:
> >> To make it clearer, I'm finding something like this:
> >> class Foo
> >> {
> >> 	int & i_;
> >> 	Foo& operator=(const Foo& rhs)
> >> 	{
> >> 		if(&rhs == this) return *this;
> >> 		i_ = rhs.i_;
> >> 		return *this;
> >> 	}
> >> }
> >>
> >> this is not accepted by my VC9 compiler.
> >>   
> >
> >It isn't? I don't see a problem (other than that it may not 
> be what you 
> >intend),
> 
> Oops, It's indeed not my intention. What I wanted is to bind 
> i_ to rhs.i_;
> 

Hi Max,
First, the C++ standard does not allow a reference to change which
object it refers to after it has been initialized. Second, I'm just
curious, why do you want to do this? Why don't you use a pointer? Or
perhaps wrap a pointer in a class with a typcast operator that produces
a reference, if you need it to have the same syntax?

Something like this:

template<class T>
class assignable_ref{

private:
    T* _pointer;
    
    
public:
    explicit assignable_ref(T& value) 
        :_pointer(&value)
    {} 
    
    operator T&() const {
        return *_pointer;
    }
    
    assignable_ref& operator=(T& rhs) {
        _pointer = &rhs;
        return *this;
    }
    
    
    assignable_ref& operator=(assignable_ref<T> const & rhs) {
        _pointer = rhs._pointer;
        return *this;
    }
};

class Foo
{
private:
        assignable_ref<int> i_;
    
public:
    Foo(int& value) : i_(value){};
    
    
        Foo& operator=(const Foo& rhs)
        {
                if(&rhs == this) return *this;
                i_ = rhs.i_;
                return *this;
        }
};

-- John