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Postings from January 2022
On Fri, Jan 21, 2022 at 11:26 AM Dave Mitchell <davem@iabyn.com> wrote:
> On Fri, Jan 21, 2022 at 03:15:31PM +0100, demerphq wrote:
> > On Fri, 21 Jan 2022 at 14:12, Nicholas Clark <nick@ccl4.org> wrote:
> >
> > > Really you want to know you have a problem *before* you call the
> callback
> > > (ie what Yves wrote - you want to be able to flag a problem at object
> > > construction time, which might well be program startup. Not fail at
> > > runtime,
> > > unattended, into a log file or even /dev/null)
> > >
> >
> > So am i correct in understanding that you would be ok with exposing an
> API
> > to check the subs arity signature? If so then I'll try to think up
> > one (others could too).
>
> But this is a general problem, not just one with signatured subs. A
> "normal" callback sub could be written as:
>
> sub callback {
> croak unless @_ == 2;
> (my $self, $foo) = @_;
> ...
> }
>
> How would the caller (say an event handler module), which has been upgraded
> to pass an optional next arg, know that the callback sub it wanted to call
> would croak on that extra arg?
>
The difference is a practical one: no one would pass a callback like your
example because it's asking for breakage and adds nothing, but most would
use a signature like ($self, $foo) in a callback documented to accept those
arguments.
-Dan
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