Branden wrote:
> I was reading RFC 271 and thinking about this pre/post handler
> thing. Why instead of having 2 subs, one for pre and other for post
> condition, and having to deal with things as strange as $_[-1], why
> don't we have only one handler that calls the real sub?
Because, by specifying the handlers separately, all the messy
implementation details are automated and hidden. A single handler would
foist them back on the programmer. One of the main uses (possibly *the*
main use) of pre and post handlers is in Design-by-Contract OO
programming, where there can be dozens or hundreds of handlers required.
And -- more compellingly -- because the inheritance semantics of
pre and post handlers are distinctly different. See:
http://dev.perl.org/rfc/271.html#Inheritance_of_postfix_handlers
http://dev.perl.org/rfc/271.html#Inheritance_of_prefix_handlers
In any case, the RFC already allows for the kind of all-in-one handlers you
suggested (and still with less coding required! ;-)
For example:
> sub abc_handler {
> my $real_abc = shift;
> do_pre_handler(@_);
> my $result = $real_abc->(@_);
> do_post_handler($result);
> return $result;
> }
is just:
pre abc {
my $real_abc = (caller(0))[10];
do_pre_handler(@_);
$_[-1] = $real_abc->(@_);
do_post_handler($_[-1]);
}
Damian
