On 24/07/2017 19:29, Viktor Sehr wrote:

I expressed myself badly perhaps, what I mean is that users cannot utilize the max value in any way. It's hidden inside the optional, meaning that any handling of the max value is undefined or throws. Perhaps even a static max member function returning (numeric_limits::max<T>() -1) should be added.

Memory is cheap; the extra tests required to throw on: optional_number<unsigned> x = 0; --x; (Or the developer headaches that would ensue if made UB and arithmetic operations occasionally make the value pop in and out of existence or do other weird things.) Are less cheap. If you're worried about wasting memory in large arrays of numbers, consider a hybrid approach where you have an array of regular integers and a bitset that separately indicates validity. This might use an extra cache line but still should perform reasonably well.

On 25 July 2017 at 16:46, Sergey Mitsyn via Boost wrote:

Also, throw on special value assignment is insane

+1

- it might be perfectly fine to pass special values to indicate something other than error - say, in a system it might be defined as a missing value (e.g. NaN meaning n/a).

And checking the that totally normal (and informative, could be a value in an enum class) return value directly is just as easy (or easier and more clear) than to have to write a try/catch block. degski -- "*Ihre sogenannte Religion wirkt bloß wie ein Opiat reizend, betäubend, Schmerzen aus Schwäche stillend.*" - Novalis 1798

Thanks for your critique, as I see boost::markable is exactly what I was intended as it is a little bit more generalized. Regarding the throwing, I intended the throw when assigned the mark value to be an "equivalent" to a assert, as I imagined the intention of assigning an uninitalized value is more clear if forced to used "val = {}" or "val.reset();", meaning it would be more of a drop-in replacement for boost::optional. /Viktor On Wed, Jul 26, 2017 at 1:41 PM Hans Dembinski via Boost < boost@lists.boost.org> wrote:

...

On 25. Jul 2017, at 15:46, Sergey Mitsyn via Boost < boost@lists.boost.org> wrote:

FYI there was a proposal recently for optional with the same purpose; unfortunately, it went nowhere:

https://lists.boost.org/Archives/boost/2015/09/225692.php

There was also boost::markable with a similar intend: https://lists.boost.org/Archives/boost/2016/09/230811.php

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