Re: [boost] Boost.Fiber review January 6-15

Le 22/01/14 17:07, Nat Goodspeed a écrit :

On Wed, Jan 22, 2014 at 7:30 AM, Vicente J. Botet Escriba wrote:

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Le 22/01/14 03:39, Nat Goodspeed a écrit :

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In my (obviously incomplete) mental model, a hypothetical fiber constructor:

fiber f(some_callable, 3.14, "a string", 17);

would be completely equivalent to:

fiber f(bind(some_callable, 3.14, "a string", 17));

What am I missing? (If this is already well-explained elsewhere, I would appreciate a pointer as much as your own explanation.) boost::bind is not movable :( or is it in C++11?) I haven't yet read Agustín's links -- but I will, thank you!

Since movable-only callables are clearly an important use case, I would hope that if (let's say) std::bind is not yet itself movable, that's a transient situation which will soon be remedied. I think that std::bind is movable.

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if you asked me to implement a variadic fiber constructor (and async() function), I would immediately forward to bind() inside each. Would that be a sufficient implementation? If not, why not? Again, the material to which Agustín points me may answer this question. But if using bind() is not an option even internally -- must Oliver (along with the author of every library that supports user callables!) reimplement bind() by hand, with support for movable types?

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A broader question to those who requested a variadic fiber constructor (and async()): is it sufficient to provide that support only when the compiler supports variadic templates, or are you asking for the whole ugly C++03 workaround as well? From my side this variadic versions must be provided for C++11 compilers at least. Any attempt to make the C++98 interface close to the C++11 would be welcome. Agustín, too, says "C++03 support would be nice." Me too. It would be nice, but not mandatory. In C++03, it is impossible to implement perfect forwarding.

Having myself implemented the preprocessor iteration for a C++03 API accepting callable-with-up-to-N-args, I know it's a bit of a pain. Moreover (a key point) anyone invoking the Fiber API who is constrained to C++03 features will not have movable-only types. In that scenario, fiber(bind(callable, arg1, arg2)) *is* completely equivalent to fiber(callable, arg1, arg2). I disagree. We have Boost/Move.

So when discussing the requested variadic fiber constructor, I will tease apart the C++11 and C++03 cases. I feel pretty comfortable stating that the former is much more important than the latter. Agreed, but at least the C++03 must support movables types.

Best, Vicente