Re: [Boost-users] [boost] Switch library review - summary of discussion so far

From: Stjepan Rajko (stipe_at_[hidden])
Date: 2008-01-12 13:42:37

On Jan 12, 2008 8:25 AM, Mathias Gaunard <mathias.gaunard_at_[hidden]> wrote:
> Stjepan Rajko wrote:
>
> > * Default default behavior
> >
> > Alexander Nasonov has also
> > indicated that a throwing default case can cause inefficiency, even
> > when it is guaranteed not to be invoked.
>
> Wouldn't an assert be more suited then?
> If default behaviour is unspecified and yet invoked, terminating sounds
> like a good thing to do.
>

An assert was considered as well - e.g., see:
http://groups.google.com.by/group/boost-list/msg/0d73059086974920

This behavior is also analogous to the standard switch statement - if
the default label is omitted, and none of the cases is matched, no
termination occurs.

>
> > There has been a lengthy discussion on the underlying design of the
> > library, what it should offer, and whether the name of the library is
> > appropriate.  There are two types of designs that have been put
> > forward as being appropriate and/or necessary for a Boost.Switch
> > library.  On one hand, there is the submitted design (labeled "A" in
> > recent postings), which takes the switch cases in an MPL sequence and
> > a single function object containing implementations of all cases.
> > Joel de Guzman has proposed another design (labeled "B"), in which the
> > switch cases are specified separately and allow a different function
> > to be used for each case.
>
> It seems to me that B is convertible to A...
> There would be no need to duplicate the interface then.
>

Under the right details, yes:
http://thread.gmane.org/gmane.comp.lib.boost.user/32628/focus=169957

Tobias offered formal transforms between the two:
http://groups.google.com.by/group/boost-list/msg/1b1fa0084cd7baad

> An utility which converts B to A would be quite useful though, even
> outside of boost.switch.
>

Thanks for your comments!

Stjepan