Re: [boost] Interest in an 'either' library?

Subject: Re: [boost] Interest in an 'either' library?
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2013-06-23 05:52:06

> -----Original Message-----
> From: Boost [mailto:boost-bounces_at_[hidden]] On Behalf Of David Sankel
> Sent: Saturday, June 22, 2013 6:47 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] Interest in an 'either' library?
> 
> Hi Larry!
> 
> On Sat, Jun 22, 2013 at 9:17 AM, Larry Evans <cppljevans_at_[hidden]>wrote:
> 
> > On 06/21/13 11:35, David Sankel wrote:
> > > **semantics**:
> > >
> > > template< typename left_type, typename right_type> struct either {
> > >   // postcondition, is_left()
> > >   either( left_type );
> > >
> > >   // postcondition, is_right()
> > >   either( right_type );
> > >
> > >   bool is_left() const;
> > >   bool is_right() const;
> > >
> > >   // postcondition, is_left()
> > >   either & operator=( left_type );
> > >
> > >   // postcondition, is_right()
> > >   either & operator=( right_type );
> > >
> > >   // precondition, is_left()
> > >   left_type left();
> > >
> > >   // precondition, is_right()
> > >   right_type right();
> > > private:
> > > };
> > >
> > > **uses**:
> > >
> > > **Use 1**: Can be used as an alternative to exceptions or the (error
> > > codes+set reference idiom):
> > >
> > > either<error_code, file_id> load_file(...);
> > >
> > > vs.
> > >
> > > error_code load_file( file_id &, ... );
> > >
> > > or
> > >
> > > // throws std::exception
> > > file_id load_file(...);
> > >
> > Isn't this like haskell's either:
> >
> >
> > http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Dat
> > a-Either.html
> 
> 
> Yes. The proposed nomenclature (either, left, right) is intentionally mimicking that of Haskell.

It's a somewhat cosmetic issue, but I suspect that most of the use cases involve an expected and an
unexpected (rather than both being equally likely), so I'm not sure that following Haskell's name is
really a good idea?

Either way, I'm in favour of this and expect it to be useful ;-)

Paul

---
Paul A. Bristow,
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[phone]  07714330204
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