Re: [boost] [ANN] type_switch with pattern matching in sandbox

From: Douglas Gregor (gregod_at_[hidden])
Date: 2003-10-20 18:47:43

On Sunday 19 October 2003 08:27 pm, Eric Friedman wrote:
> This is something I had been working on about two months ago but didn't
> post to the sandbox until recently.
>
> The basic idea is this:
>
>    switch_( [variant] )
>
>      |= case_< [pattern1] >(...)
>      |= case_< [pattern2] >(...)
>      |
>      |= default_(...)  // optional catch-all
>
>      ;
>
> The switch_ will fail to compile if not every case is handled. In terms
> of handling, the case_ constructors take typical function objects,
> though the switch_ ignores any return values.

I would absolutely love to see this in the library. A while back (pre-variant) 
I prototyped something similar for 'any' (with 'tuple' for product types) 
that may be of interest:
  http://article.gmane.org/gmane.comp.lib.boost.devel/311/match=typeswitch

The only things it did that I'd like to see in your version are:
  1) Support for return types, as Brian already mentioned. I think this is 
crucial.

  2) I think I like putting the set of cases in brackets, but it's probably 
Ocaml-envy kicking in:

switch_([variant])[
  case_<[pattern1]> (...)
  | case_<[pattern2]> (...)
  | ...
  | default_(...)
  ;

The syntactic bit is, of course, trivial and unnecessary. Pick whatever syntax 
you like.

        Doug