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Subject: Re: [boost] Weak functor: Interested? (How to boost::bind to a weak_ptr)
From: Vladimír Tøebický (vladimir.trebicky_at_[hidden])
Date: 2012-01-11 04:46:42

On Wed, Jan 11, 2012 at 10:38 AM, Roman Perepelitsa
<roman.perepelitsa_at_[hidden]> wrote:
> 2012/1/11 Vladimír Třebický <vladimir.trebicky_at_[hidden]>
>> On Wed, Jan 11, 2012 at 9:19 AM, Roman Perepelitsa
>> <roman.perepelitsa_at_[hidden]> wrote:
>> > It can be done. In fact, it has already been done. See
>> >
>> Nice. I like this. However, once you declare the get_pointer (plus
>> ptr_adater and invoker) there's no way to specify what should happen
>> if lock() returns empty shared_ptr. In the example "invoker" returns
>> default value:
>> R operator()() const
>> {
>>  return ci_.first ? (ci_.first->*ci_.second)() : R();
>> }
>> which may (a) not be possible (if R is not default-constructible) or
>> (b) not desired (eg. if user wants an exception to be thrown).
>> Do you think there would be a way to control the behavior?
>  In this case one will have to use something like boost::weak_fn or write
> the trampoline function manually.
> void do_something(const weak_ptr<foo>& p) {
>  // Complete freedom here.
>  if (shared_ptr<foo> sp = p.lock())
>    sp->do_something();
>  else
>    throw "expired weak_ptr";
> }
> bind(do_something, my_weak_ptr)();

Sure, that's always a way. Once you start having a lot of callbacks it
may become messy.

> In practice, however, I only ever used void-returning functors with
> weak_ptr.

Agreed, me to. But typically I need the callbacks to either silently
do nothing or throw.

Anyway, the question is whether such a tool may find place in Boost
for people looking for this kind of behavior, wdyt?


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