Subject: Re: [boost] [variant] Maintainer
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2015-06-28 12:17:34
On 28 Jun 2015 at 18:03, Bjorn Reese wrote:
> >> Empty => False
> >> Value => True
> >> Errored/Excepted => Indeterminate
>
> It seems more intuitive to me if Empty returns Indeterminate and
> Errored returns False.
In a Kleene logic, false < unknown < true for AND, so for variant if
you wanted error && empty to equal empty, you'd choose the scheme
above. If you wanted error && empty to equal error, you'd choose your
scheme.
For lightweight monad and future, I've gone for empty being dominant.
This was not an easy choice to make, and I am still unsure if it is
correct.
For variant it's that much harder again. I am currently totally
undecided personally on that one.
Niall
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