Caching

• Caching is a common strategy for speeding up a pure function

• The first time you call it, it remembers its return value

• If you call it again with the same arguments, it returns the cached value

          {  my @fact = ();
             sub factorial {
               my $n = shift;

               return $fact[$n] 
                 if defined $fact[$n];

               $fact[$n] = 
                 ($n == 0 ? 1 
                          : $n * factorial($n-1));
           }
         }

• There aren't that many simple good ideas

  • Caching is one

  • As a result, it is used everywhere

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Copyright © 2003 M. J. Dominus