How to convert an array_ref: 
$aref = ['a', 'b', 'c', 'd'];

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Into an hash ref such as: 
$href = {  'a' => {
                   'b' => {
                            'c' => {
                                     'd' => 1
                                   }
                           }
                   },
         };

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In reply to Change array to tiered hashref - brain teaser by jonathan415

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