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Subject: Re: [boost] [optional] Safe optional
From: Sylvester-Bradley, Gareth (Gareth.Sylvester-Bradley_at_[hidden])
Date: 2014-11-20 11:29:00

On Nov 20, 2014 at 16:13, Bjorn Reese wrote:
> On 11/20/2014 11:49 AM, Andrzej Krzemienski wrote:
> > The user-provided int can be any value of int plus the situation where user
> > decides not to type any input. the latter is a valid and useful
> > information. E.g. when an int represents some threshold, having boost::none
> > means "go with no threshold". boost::none is just a value. this in turn
> > implies the implicit conversions:
> >
> > optional<int>() != 2;
> >
> > The above is logical and useful, even outside of the containers.
> As optional is a nullable type, it could be useful to let the comparison
> operators return a tri-bool instead of a bool.

There are a number of well-trodden paths for these kind of comparisons...
optional(none) could be 'bottom' as it is now,
or follow the example of IEEE floating point NaN,
or follow three value logic like NULL in SQL.
I think those are all differently sensible, and there are probably more...

Best regards,

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