<?php
$dictionary['Opportunity']['fields']['your_autoincrement_field'] = array (
    'required' => true,
    'name' => 'your_autoincrement_field',
    'vname' => 'LBL_YOUR_AUTOINCREMENT_FIELD',
    'type' => 'int',
    'massupdate' => 0,
    'comments' => 'Automatically generated number field',
    'help' => 'User friendly description of field',
    'importable' => 'true',
    'duplicate_merge' => 'disabled',
    'duplicate_merge_dom_value' => '0',
    'audited' => false,
    'reportable' => true,
    'calculated' => false,
    'auto_increment'=> true,
);
$dictionary['Opportunity']['indices']['your_autoincrement_field'] = array(
    'name' => 'your_autoincrement_field',
    'type' => 'unique',
    'fields' => array(
        'your_autoincrement_field'
    ),
);
?>