Symfony 2 configuration: array of dynamic associative arrays

config.yml

acme_demo:
    transitions:
        - { hc_cba: 180 }
        - { cba_hc: -1 }

DynarrayConfiguration.php

<?php
$rootNode
    ->children()
        ->arrayNode('state_machine')
            ->requiresAtLeastOneElement()
            ->beforeNormalization()
                ->ifArray()
                    ->then(function($values) {
                        $ret = array();

                        foreach ($values as $value) {
                            foreach ($value as $transition => $time) {
                                $ret[] = array('transition' => $transition, 'time' => e);
                            }
                        }

                        return $ret;
                    })
                ->end()
                ->prototype('array')
                ->children()
                    ->scalarNode('transition')->end()
                    ->scalarNode('time')->end()
                ->end()
            ->end()
        ->end()
    ->end()
;