Twig：如何检查变量是否是DateTime对象[重复]

I have to check if a variable is a DateTimeobject or a simple string to use it in my template.

If the variable is a DateTime, I have to format it as a date; simply print it if is a string.

{% if post.date is DateTime %}
    {% set postDate = post.date|date %}
{% else %}
    {% set postDate = post.date %}
{% endif %}

<p>Il {{ postDate }}

I think I should do this using a Twig Test (as also suggested in this StackOverflow Answer about arrays), but I don't well understand in which folder of my Symfony App I should put the code and how to register it in the application.

Once wrote the test, how can I use it in my Twig templates in Symfony?

</div>

You should create a twig function

AcmeBundle\Twig\CheckExtension.php

<?php
namespace AcmeBundle\Twig;

class CheckExtension extends \Twig_Extension
{
    public function getFunctions() {
        return array(
            'isDateTime' => new \Twig_Function_Method($this, 'isDateTime'),
        );
    }

    public function isDateTime($date) {
        return ($date instanceof \DateTime); /* edit */
    }

    public function getName()
    {
        return 'acme_check_extension';
    }
}

services.yml

services:
    acme_check_extension:
        class: AcmeBundle\Twig\CheckExtension
        tags:
            - { name: twig.extension }

in your template:

{% if isDateTime(post.date) %} 
    ...
{% endif %}