Re: [boost] customizing boost::function

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-12-13 20:36:52

Theodore Witkamp wrote:

> If you notice it's my_weak_ptr not boost::weak_ptr. Which can be used
> in this way due to the implementation of get_pointer for that type.

This is dangerous since you may be left with a dangling this if something 
invalidates the weak pointer while you're inside f, but you probably knew 
that. (This is the reason why boost::weak_ptr can't be used in this way.)

The "no exceptions" constraint makes it harder than it needs to be. In this 
situation I would probably use a null X object:

struct Xb
{
    virtual void f() = 0;
};

struct Xn: Xb
{
    void f() {} // stub
};

Xn nx;

struct X: Xb
{
    void f(); // do real work
};

Xb * lock( my_weak_ptr<Xb> px )
{
    return px? get_pointer( px ): &nx;
}

int main()
{
    my_shared_ptr<Xb> px( new X );
    my_weak_ptr<Xb> wp( px );

    function<void()> f = bind( &Xb::f, bind( lock, wp ) );

    f();

    px.reset();

    f();
}

or something like that. Obviously untested. :-)