constant

constant 检查变量的值是否与常量完全相同。可以使用全局常量或类常量：

{% if post.status is constant('Post::PUBLISHED') %}
    the status attribute is exactly the same as Post::PUBLISHED
{% endif %}

也可以从对象实例测试常量：

{% if post.status is constant('PUBLISHED', post) %}
    the status attribute is exactly the same as Post::PUBLISHED
{% endif %}