gistfile1.php

<?php

// tested on php 5.4.4 on freebsd
// tested on php 5.5.9 on windows

// rename the error routes to e403 and e404, and this does not happen.
// -or-
// $array = get_object_vars($object->ErrorRoutes);

$json = <<< 'EOF'
{
	"Namespaces": [
	],
	"Commonspace":"Routes\\Common",
	"ErrorRoutes": {
		"403": "Routes\\Error\\Forbidden",
		"404": "Routes\\Error\\NotFound"
	}
}
EOF;

// decode an object which has a property which is an object...
$object = json_decode($json);
var_dump($object);

// but we want that object to be an assoc array because those properties are
// not accessable without special syntax due to them starting with a number...
$array = (array)$object->ErrorRoutes;
var_dump($array);

// then we try to access them...
var_dump(
	array_key_exists(404,$array),
	array_key_exists("404",$array)
);

/*
C:\Users\bob\Desktop>php test.php

object(stdClass)#1 (3) {
  ["Namespaces"]=>
  array(0) {
  }
  ["Commonspace"]=>
  string(13) "Routes\Common"
  ["ErrorRoutes"]=>
  object(stdClass)#2 (2) {
    ["403"]=>
    string(22) "Routes\Error\Forbidden"
    ["404"]=>
    string(21) "Routes\Error\NotFound"
  }
}

array(2) {
  ["403"]=>
  string(22) "Routes\Error\Forbidden"
  ["404"]=>
  string(21) "Routes\Error\NotFound"
}

bool(false)
bool(false)
*/