On Tue, Dec 10, 2002 at 01:53:28PM +1100, Damian Conway wrote:
> And in those rare cases where you really do need partial caching, the
> simplest solution is to split the partially cached subroutine into a
> fully cached sub and an uncached sub:
>
> sub days_in_month(Str $month, Int $year)
> {
> $month = lc $month;
> if $month eq 'feb'
> {
> my sub feb_days (Int $year) is cached {
> my $leap = $year % 4 == 0
> && ($year % 100 != 0 || $year % 400 == 0);
> return $leap ? 29 : 28;
> }
> return feb_days($year);
> }
>
> else
> {
> # Simple look-up, so caching would be counter-productive:
> return %days{$month}; # %days was declared above (honest)
> }
> }
I don't think that works correctly. This will create a new cached
sub each time $month eq 'feb'? That'll generate a lot of cached
subs, values will be calculated each time $month eq 'feb, and none
of the values will ever be returned from any of those caches.
Schwern's approach of factoring out days_in_feb into a cached sub
is the same basic idea, and doesn't have this issue.
Z.
