$i?$i=1:$i=0;

Puh-lease, use some whitespace! Here are some alternatives:

$i ? $i = 1 : $i = 0;
$i = $i ? 1 : 0;

$i = !!$i || 0;

$foo = $foo ? 1 : 0; # Single-letter variable names:
                     # easy to type, hard to read
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Always pass referances not data structures

Most references are the root of data structures, so I think you meant "Always pass references instead of flattened hashes or lists". Note that you can't use this if the sub in question doesn't expect it.

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