做逻辑判断的。目前支持的有
divisibleby null even odd sameas constant defined empty
divisibleby
检查是否能被整除
{% if loop.index is divisibleby(3) %}
...
{% endif %}
{% if loop.index is divisibleby(3) %}
...
{% endif %}
null
{{ var is null }}
{{ var is null }}
even
变量是否是偶数{{ var is even }}
{{ var is even }}
odd
变量是否是奇数
{{ var is odd }}
{{ var is odd }}
sameas
检查变量的地址是否相同
{% if foo.attribute is sameas(false) %}
the foo attribute really is the ``false`` PHP value
{% endif %}
{% if foo.attribute is sameas(false) %}
the foo attribute really is the ``false`` PHP value
{% endif %}
constant
检查变量的值是否相同
{% if post.status is constant('Post::PUBLISHED') %}
the status attribute is exactly the same as Post::PUBLISHED
{% endif %}
{% if post.status is constant('Post::PUBLISHED') %}
the status attribute is exactly the same as Post::PUBLISHED
{% endif %}
defined
测试变量是否定义
{# defined works with variable names #}
{% if foo is defined %}
...
{% endif %}
{# and attributes on variables names #}
{% if foo.bar is defined %}
...
{% endif %}
{% if foo['bar'] is defined %}
...
{% endif %}
{# defined works with variable names #}
{% if foo is defined %}
...
{% endif %}
{# and attributes on variables names #}
{% if foo.bar is defined %}
...
{% endif %}
{% if foo['bar'] is defined %}
...
{% endif %}
empty
测试变量是否为空，empty的意思是：该变量已经定义，但他的值是 null false 或者是空字符串
{# evaluates to true if the foo variable is null, false, or the empty string #}
{% if foo is empty %}
...
{% endif %}
摘自 jiaochangyun的专栏
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