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Subject Author Date
Accessing the Memoize cache Daniel E. Macks 04-02-2005
Posted by Daniel E. Macks on April 2, 2005, 1:15 am
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I have an expensive function my_cmp that I'd like to Memoize. Is
there any way I can take advantage of the property that
my_cmp($a,$b) == - my_cmp($b,$a)
so if my_cmp is called with the same args as before but swapped I
don't have to redo the "actual" my_cmp function?

Conceptually I'd like to either check if the swapped-arg form has
already been Memoized:
my_cmp {
if ( Memoize::seen('my_cmp', [reverse @_]) ) {
$result = -&my_cmp(revese @_);
} else {
$result = # expensive operations
}
return $result;
}

Or force the swapped-arg form into the Memoize cache:
my_cmp {
my $result = # expensive operations
Memoize::cache('my_cmp', [reverse @_], -$result);
return $result;
}

Is there a clean way to do either of these solutions, or is there some
other existing solution I haven't found?

dan

--
Daniel Macks
dmacks@netspace.org
http://www.netspace.org/~dmacks



Posted by Felix Geerinckx on April 2, 2005, 4:49 am
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On 02/04/2005, Daniel E. Macks wrote:

> I have an expensive function my_cmp that I'd like to Memoize. Is
> there any way I can take advantage of the property that
> my_cmp($a,$b) == - my_cmp($b,$a)
> so if my_cmp is called with the same args as before but swapped I
> don't have to redo the "actual" my_cmp function?

You could write

sub my_cmp {
my ($x, $y) = @_;
return $x<$y ? my_cmp2($x, $y) : -my_cmp2($y, $x);
}

and then Memoize my_cmp2.
--
felix


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