Re: [boost] customizing boost::function

From: Theodore Witkamp (ted_at_[hidden])
Date: 2006-12-13 21:10:00

I thought about using a Null object but I think that would be too much
of a burden. Given that the stub functions would need to be
non-trivial in may cases because of the return types.
And because my platform support cooperative multi threading not
preemptive multi threading i can get away only locking when I call the
function.

I have my own non-boost smart pointers and function objects and i can
call Func<>.isNull()
on them and it does what I want. However I long for the convenience of bind.
So I am left with a dilemma should I add more functionality to Func or
add what I need to boost::function.

Thanks

On 12/13/06, Peter Dimov <pdimov_at_[hidden]> wrote:
> 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. :-)
>
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-- 
Theodore Witkamp
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