Re: [boost] [tribool] short-circuting issue with overloads of operator|| and operator&&

From: Corrado Zoccolo (czoccolo_at_[hidden])
Date: 2008-05-21 02:57:56

On Tue, May 20, 2008 at 4:13 PM, klaus triendl <klaus_at_triendl.eu> wrote:
>
>
> Hmm, I didn't look thoroughly at it but wouldn't it be possible to
> remove these overloads?
> I've seen a proposal for bool_set that doesn't overload (anymore) the
> two logical operators.
>

I don't think you can get rid of the overloads.
The overloads are needed to implement the truth tables (see
http://www.boost.org/doc/libs/1_35_0/doc/html/boost/logic/operator_id257657.htmland
http://www.boost.org/doc/libs/1_35_0/doc/html/boost/logic/operator!_id340819.html
).

In order to remove them, you need a conversion C: tribool-> bool that
preserves all the truth tables, and is an homomorphism, i.e.
C( op(X) ) == op( C(X) ) and C( X op Y ) == C(X) op C(Y)

Unfortunately, if such conversion existed, then :
C(indeterminate) = C(!indeterminate) = !C(indeterminate)
that is impossible for a bool.

Do you really need tribool semantics, or you just needed something like
optional<bool>?

One thing that can be done is to use expression templates to build the
operator expressions, and implement short circuit evaluation on top of them,
but then you have to pay attention to how you build your expression, because
you have to explicitly delay expressions like *a_bool_pointer.

Corrado

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> Klaus
>
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__________________________________________________________________________
dott. Corrado Zoccolo mailto:czoccolo_at_[hidden]
PhD - Department of Computer Science - University of Pisa, Italy
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