Examples of Tricky Features

Memoization

     my %cache;        
     wrap 'myfunction', 
        pre => sub { $_[-1] = $cache{$_[0]} if defined $cache{$_[0]} },
       post => sub { $cache{$_[0]} = $_[-1] };

• The regular function arguments are passed to the wrappers

  • An extra argument is appended to the end of @_

  • It contains the function's return value

  • Assigning to $_[-1] overwrites the return value

  • If you do this in a prewrapper, the original function is never called at all

Next

Copyright © 2003 M. J. Dominus