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Subject: Re: [boost] Futures - wait callback with a user specific parameter.
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2009-01-20 09:06:16

"vicente.botet" <vicente.botet_at_[hidden]> writes:

> From: "vicente.botet" <vicente.botet_at_[hidden]>

>> Currently the wait callback parameter is either a promise or packaged_task
>> template<typename F>
>> void set_wait_callback(F f);
>> prom.set_wait_callback(f); // will call f(&prom)
>> task.set_wait_callback(f); // will call f(&task)
>> I would like to have a wait callback with a user specific parameter.
>> template<typename F,typename U>
>> void set_wait_callback(F f,U* u); // will call f(u)
>> prom.set_wait_callback(f, x); // will call f(x)
>> The use case is a class that contains a promise and wants to
>> provide a set_wait_callback. Which parameter will have the wait
>> calback? A promise. But the user is not aware that my class has
>> promise, and he will surely want to have as parameter a pointer to
>> my class. So the simpler is to provide a user specific parameter
>> that is defaulted to instance providing the wait_callback setting.
>> Of course my class can wrap the user function and the class instance
>> template <typename R>
>> class X {
>> template <typename F>
>> static void wait_callback_wrapper(promise<R>* p, F f, X*x) {
>> f(x);
>> }
>> template<typename F>
>> void set_wait_callback(F f) {
>> prom_.set_wait_callback(bind(wait_callback_wrapper, _1, f, this));
>> }
>> };
>> But this implies much more resources, two binds instead of one.
>> Could this be added without to much trouble?

It could, but....

> Anthony, I've find this on one your posts:
>>> At the moment, I've specified the callbacks as taking a
>>> non-const reference to the promise or packaged_task for which they are set,
>>> but I'm open to just making them be any callable function, and leaving it up
>>> to the user to call bind() to do that.
> Anthony, I think that just a callable function will be the best option.

.... I think this is the best option.


Anthony Williams            | Just Software Solutions Ltd
Custom Software Development |
Registered in England, Company Number 5478976.
Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL

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