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return $fib3_cache{$n} ||= do {

I'd strongly recommend trading //= for ||=. Any function that can return 0, but costs to determine that, looses out as is.

You can get greater benefits still for functions that take low integers as inputs by using an array instead of a hash for the cache:

my @fib4_cache; sub fib4 { my $n = shift; return $fib4_cache[$n] //= do { $n < 2 ? $n : fib4($n-1) + fib4($n-2) }; } __END__ C:\test>memofib.pl Rate fib1 fib2 fib3 fib4 fib1 88.7/s -- -100% -100% -100% fib2 219835/s 247838% -- -89% -91% fib3 2073455/s 2338415% 843% -- -19% fib4 2551114/s 2877136% 1060% 23% --

And see the benefits more clearly if you do away with some of the benchmark overheads by loosing the sub wrappers (The module adds its own wrapper internally):

cmpthese(-1, { fib1 => q{ fib1 20 }, fib2 => q{ fib2 20 }, fib3 => q{ fib3 20 }, fib4 => q{ fib4 20 }, }); __END__ C:\test>memofib.pl Rate fib1 fib2 fib3 fib4 fib1 87.4/s -- -100% -100% -100% fib2 223254/s 255377% -- -89% -91% fib3 2071504/s 2370384% 828% -- -20% fib4 2579867/s 2952119% 1056% 25% --

And finally, there's a couple more % to be had:

my @fib5_cache; sub fib5 { my $n = shift; return $fib5_cache[ $n ] //= do { $n < 2 ? $n : ( $fib5_cache[ $n-1 ] //= fib5($n-1) ) + ( $fib5_cache[ $n-2 ] //= fib5($n-2) ) ## corrected; thanks +to moriitz }; } __END__ C:\test>memofib.pl Rate fib1 fib2 fib3 fib4 fib5 fib1 89.0/s -- -100% -100% -100% -100% fib2 218452/s 245352% -- -89% -91% -91% fib3 2022174/s 2272005% 826% -- -18% -20% fib4 2478824/s 2785096% 1035% 23% -- -2% fib5 2537045/s 2850512% 1061% 25% 2% --

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In reply to Re: Reminder to self: must use Memoize more often! by BrowserUk
in thread Reminder to self: must use Memoize more often! by tobyink

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