Re: [boost] [coroutine] Experimenting with interfaces

Subject: Re: [boost] [coroutine] Experimenting with interfaces
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2012-09-21 14:59:13

Am 21.09.2012 20:09, schrieb Giovanni Piero Deretta:
> On Fri, Sep 21, 2012 at 6:34 PM, Oliver Kowalke <oliver.kowalke_at_[hidden]>wrote:
>
>> Am 21.09.2012 19:17, schrieb Eugene Yakubovich:
>>
>>   [snipped example with coroutine-fn having void result]
>>
>> I'm not sure what this means for the best interface but I did want to
>>> share these thoughts and examples.
>>>
>> thank you for your examples:
>> If coroutine's template signature returns a type different from void it is
>> required that the coroutine function does return the same type instead of
>> void as in your example.
>>
>>
>> template <typename C>
>> void timer(C c, chrono::seconds interval) {
>>    //  while( interval != chrono::seconds::zero() ) {
>>    //      this_thread::sleep_for(**interval);
>>    //      interval = c(interval);
>>    //  }
>>
>> }
>>
>> coroutine<chrono::seconds(**chrono::seconds)> c(
>>      [](coroutine<chrono::seconds(**chrono::seconds)> c, chrono::seconds
>> i) {
>>          timer(c, i);
>>      }
>> );
>>
>> chrono::seconds s = c(chrono::seconds(1)); // [1]
>>
>>
>> Which value has variable 's' after return from 'c(chrono::seconds(1))' ?
>>
> for seconds(1), it would simply return seconds(1), right? If you mean on
> chrono::seconds::zero(), then the coroutine would return without yielding
> any result. In this case, an option that would allow mantaining the
> function-like interface would be to throw an exception from [1], or, if
> operator() was called with std::nothrow as an additional first parameter,
> return an optional. This was what the original library did on exceptional
> returns and would work well here as well I guess. Note that 'coroutine'
> could detect the result type of the coroutine-fn and decide what to do on
> return depending on it, this way the user can decide the most natural
> behaviour depending on the nature of the problem.
>
if the the coroutine function is forced to return the return type of the 
signature no exception must be thrown and optional is also not necessary.

template <typename C>
void timer(C c, chrono::seconds interval) {
     while( interval != chrono::seconds::zero() ) {
         this_thread::sleep_for(**interval);
         interval = c(interval);
     }
     return interval;
}

coroutine<chrono::seconds(**chrono::seconds)> c(
     [](coroutine<chrono::seconds(**chrono::seconds)> c, chrono::seconds
i) {
         timer(c, i);
     }
);

chrono::seconds s = c(chrono::seconds(1));
s = c(2*s);
s = c(3*s);
s = c(5*s);