Re: [boost] [outcome] Ternary logic -- need an example

Subject: Re: [boost] [outcome] Ternary logic -- need an example
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2017-05-15 18:18:40

2017-05-15 17:57 GMT+02:00 Niall Douglas via Boost <boost_at_[hidden]>:

> >> This argument can be generalised into the argument in favour of ternary
> >> logics over binary logics. Sure, 90% of the time binary logics are
> >> sufficient, but binary is a subset of ternary. And *you don't have to
> >> use* the "other" state in a ternary logic just because it's there. Just
> >> don't use it, so long as its implementation signals its unintentional
> >> usage with a very loud bang, it's a safe design.
> >>
> >> (There is an argument that Outcome's "very loud bang" isn't loud enough.
> >> I'd be pleased to hear feedback on that)
> >
> > Niall, you mention "ternary logic" here, and I guess it has to do with
> > 'module' `tribool` exposed by Outcome library. But I do not believe I
> have
> > seen in the documentation (I mean the tutorial section) how I am supposed
> > to use it, and how it improves my programs. Or I might have just missed
> it.
> > Could you give me an example?
>
> It doesn't have much to do with tribool. outcome<T> and result<T>
> deliberately take a three state based design with an explicit choice of
> ternary instead of binary state. The original motivation was actually
> for the basic_monad based, since removed, non-allocating future-promise
> implementation where we needed a third state to indicate "pending", but
> it turned out to be very useful in itself for simplifying usage,
> eliminating writing boilerplate, and acting as an out-of-band signalling
> mechanism.
>

Ok, so by "ternary" you mean "eihter value, or error, or just nothing". But
still, in the documentation we can see the "module"
`boost_lite::xxx::tribool`:
https://ned14.github.io/boost.outcome/group__tribool.html
Does this document only an implementation detail? If so, maybe you should
dropit from documentation, as it suggests that tribool is part of Outcome's
interface.
Or maybe it is part of Outcome's interface?
Also, what do you understand by "module" here?

Regards,
&rzej;