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

-----Original Message----- From: Boost [mailto:boost-bounces@lists.boost.org] On Behalf Of David Sankel Sent: Saturday, June 22, 2013 6:47 PM To: boost@lists.boost.org Subject: Re: [boost] Interest in an 'either' library?

Hi Larry!

On Sat, Jun 22, 2013 at 9:17 AM, Larry Evans 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 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, Prizet Farmhouse, Kendal LA8 8AB UK +44 1539 561830 07714330204 pbristow@hetp.u-net.com