<?php

$obj = [
    'a' => function(){ return 1; },
    'b' => [
      'ba' => function(){ return 2; },
      'bb' => [
        'bba' => function(){ return 3; }
      ]
    ]
];

var_dump($obj['a']());
var_dump($obj['b']['ba']());
var_dump($obj['b']['bb']['bba']());