badfile.php

<?php

namespace Symfony\Component\Yaml;

class Yaml 
{

	public static function dump()
	{
		die( 'Bad File' );	
	}
}

composer.json

{
    "name": "jorbin/namespaces",
    "authors": [
        {
            "name": "Aaron Jorbin",
            "email": "aaron@jorb.in"
        }
    ],
    "require": {
        "symfony/yaml": "^3.1"
    }
}

composer.lock

{
    "_readme": [
        "This file locks the dependencies of your project to a known state",
        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
        "This file is @generated automatically"
    ],
    "hash": "b87a6ab585e97e78a80b1819c3c2956a",
    "content-hash": "8657dae39e95a86827d152758b4497c6",
    "packages": [
        {
            "name": "symfony/yaml",
            "version": "v3.1.3",
            "source": {
                "type": "git",
                "url": "https://github.com/symfony/yaml.git",
                "reference": "1819adf2066880c7967df7180f4f662b6f0567ac"
            },
            "dist": {
                "type": "zip",
                "url": "https://api.github.com/repos/symfony/yaml/zipball/1819adf2066880c7967df7180f4f662b6f0567ac",
                "reference": "1819adf2066880c7967df7180f4f662b6f0567ac",
                "shasum": ""
            },
            "require": {
                "php": ">=5.5.9"
            },
            "type": "library",
            "extra": {
                "branch-alias": {
                    "dev-master": "3.1-dev"
                }
            },
            "autoload": {
                "psr-4": {
                    "Symfony\\Component\\Yaml\\": ""
                },
                "exclude-from-classmap": [
                    "/Tests/"
                ]
            },
            "notification-url": "https://packagist.org/downloads/",
            "license": [
                "MIT"
            ],
            "authors": [
                {
                    "name": "Fabien Potencier",
                    "email": "fabien@symfony.com"
                },
                {
                    "name": "Symfony Community",
                    "homepage": "https://symfony.com/contributors"
                }
            ],
            "description": "Symfony Yaml Component",
            "homepage": "https://symfony.com",
            "time": "2016-07-17 14:02:08"
        }
    ],
    "packages-dev": [],
    "aliases": [],
    "minimum-stability": "stable",
    "stability-flags": [],
    "prefer-stable": false,
    "prefer-lowest": false,
    "platform": [],
    "platform-dev": []
}

index.php

<?php
require 'vendor/autoload.php';
require 'badfile.php';

use Symfony\Component\Yaml\Yaml;

$array = array(
	'foo' => 'bar',
	'bar' => array('foo' => 'bar', 'bar' => 'baz'),
);

var_dump( Yaml::dump($array) );