Re: [boost] [gsoc-2013] Boost.Expected

Subject: Re: [boost] [gsoc-2013] Boost.Expected
From: Rob Stewart (robertstewart_at_[hidden])
Date: 2013-04-28 17:28:39

On Apr 28, 2013, at 2:17 PM, "Pierre T." <ptalbot_at_[hidden]> wrote:

> On 04/28/2013 07:30 PM, Vicente J. Botet Escriba wrote:
>> 
>>>> Yes this is quite similar if we had exceptions and we had a try/catch block
>>>> 
>>>> f0().then(f1).then(f2).then(f3).visit_error(error_visitor);
>>>> 
>>>> try {
>>>>  f3(f2(f1(f0())));
>>>> } catch(...) {
>>>>  error_visitor();
>>>> }

When the chain gets long, try blocks make increasing sense.

>>>> It would be great if we could have the equivalent for
>>>> try {
>>>>  h(f(), g());
>>>> } catch(...) {
>>>>  error_visitor();
>>>> }
>>>> 
>>>> when_all(f(), g()).then(h).visit_error(error_visitor);

"if_all" seems better than "when_all".

[snip]

>>>> I think we could just do the following:
>>> 
>>> e.then(f, g).then(h).inspect(error_inspector)

"inspect" doesn't carry much meaning in context.

[snip]

>>> About the "inspect" method, I try to find another name instead of visit_error because it makes me think to the pattern visitor which is
>>> too specific to hierarchy classes. I found that inspect was nice because it's like in a factory where the chief "inspects" that everything has been alright.
>>> 
>> The name should work independently of the name of the 'then()' function.
> Oh nice remark.

+1

>> on_exception? if_exception? catch_all? capture?
>> 
>> e.catch_all(eh);
>> 
>> And maybe catching/capturing an exception type at a time.
>> 
>> e.catch_one<E1>(e1).catch_one<E2>(e2).catch_all<EA>(eh);
>> 
>> e.capture<E1>(e1).capture<E2>(e2).capture<all>(eh);
>> 
>> But a C++ try/catch is not worst, or is it?
>> 
>> try { v=e.get(); } catch(E1 & ex) { e1(ex); } catch(E2 & ex) { e2(ex); }
>> catch(...) {}
>> 
> I would say "on_error", so it would be a generic name for error type that aren't exception.

"on_error" seems fine. It reminds me, however, of functions overloaded to take system_error to avoid exceptions. IOW, rather than passing a function, one passes the exception type to collect the error.

___
Rob

(Sent from my portable computation engine)