How to safely access array indices after splitting with the `split` filter to avoid 'out of range' errors?

In the template development of AnQi CMS,splitThe filter is undoubtedly a very practical tool.It can help us easily split a string containing a specific delimiter (such as multiple keywords or tags) into an array that can be traversed and accessed.However, the challenge that follows is how to safely access the elements in these arrays, avoid common "out of range" errors, which, once they occur, can either partially fail to display the page content or cause the entire page to render failure, affecting user experience.

This article will delve into several safe access methods in the AnQi CMS templatesplitThe method of filtering arrays, which helps you write more robust and user-friendly template code.

UnderstandingsplitBasic usage and potential risks of filters

First, let's reviewsplitThe principle of the filter. Imagine you have a string, such as multiple tags of a product, separated by commas, like this:"时尚,潮流,舒适"In the template, you can usesplitThe filter converts it into an array:

{% set tags = product.Tags|split:"," %}

At this time,tagsThe variable becomes a container containing["时尚", "潮流", "舒适"]an array. We might naturally think of usingtags[0]/tags[1]This way to access the first or second element in an array. This direct index access method is no problem when the array is determined to have an element at that index position.

However, the risk exists in the scenario of 'uncertainty'. If the original string is empty, or the delimiter does not exist, or even if it only contains one element, then it can be accessed directly.tags[2]This kind of index exceeding the actual length of the array will cause an error of 'out of range' during template rendering. For example, ifproduct.TagsIs"时尚"thentagsthe length of the array is 1, trying to accesstags[1]will result in an error.

In order to avoid this situation, we need to introduce some security check mechanisms in the template.

Security access strategy one: Check the length of the array before accessing.

The most direct and safest method is to check the actual length of the array before trying to access the array elements. The Anqi CMS template engine provideslengthA filter that can easily get the number of elements in an array. CombinedifA logical judgment tag, ensuring that only existing indices are accessed.

For example, if you only need to access the first and second elements of the array:

{% set tags = product.Tags|split:"," %}

{# 访问第一个元素前，检查数组长度是否大于0 #}
{% if tags|length > 0 %}
    <p>第一个标签：{{ tags[0]|trim }}</p> {# 加上trim去除可能的多余空格 #}
{% else %}
    <p>暂无标签</p>
{% endif %}

{# 访问第二个元素前，检查数组长度是否大于1 #}
{% if tags|length > 1 %}
    <p>第二个标签：{{ tags[1]|trim }}</p>
{% endif %}

This method is clear and straightforward, by explicitly checking the length of the array, it can effectively avoid out-of-bound errors. At the same time, we can alsoelseBranch provides alternative content or prompts to enhance user experience. It is worth mentioning that usingtrimThe filter processes each element after the split is a good habit because there may be extra whitespace before and after the delimiter in the original string (for example"标签1, 标签2"After splitting, we get["标签1", " 标签2"])trimCan help us remove these unnecessary spaces.

Security access strategy two: Use loop structures to traverse the array.

For scenarios where all elements in an array need to be processed, or the number of elements is uncertain, usingforLoops are a more elegant and safe approach. The Anqi CMS template engine supportsfor...emptyStructure, this allows you to provide a friendly prompt when the array is empty, avoiding a blank page.

UseforLoops, you do not need to manually check if each index exists, the loop itself will handle the boundary issues:

{% set tags = product.Tags|split:"," %}

<p>文章标签：</p>
<ul>
{% for tag in tags %}
    {# 在循环中，直接使用循环变量tag，并进行trim处理 #}
    <li>{{ tag|trim }}</li>
{% empty %}
    {# 如果tags数组为空，则显示这里的内容 #}
    <li>暂无相关标签</li>
{% endfor %}
</ul>

This method is not only safe, but also the code is more concise, especially suitable for displaying dynamic quantity content such as tag lists, image groups, etc.emptyThe existence of blocks allows you to flexibly provide alternatives for situations without content, avoiding empty pages.

Safety access strategy three: combinesliceRange control with filters

sliceThe filter provides a more refined control method, even if you only want to retrieve elements at specific positions, it can also ensure that the operation does not exceed the array boundary and return a safe sub-array.sliceis used forobj|slice:"from:to"it will return a new sub-array. If the specified range is beyond the boundary of the original array,sliceit will automatically adjust, only returning the available part without throwing an error.

For example, if you want to get the first element of an array but also want to ensure that there is no error if the array is empty:

`twig {% set tags = product.Tags|split:`,` %}

Use slice to get a sub-array containing at most one element

{% if firstTagArray %}

<p>第一个标签（通过slice）：{{ firstTagArray[0]|trim }}</p>

{% else %}

<p>没有第一个标签。</p>

{% endif %}

{# Similarly obtain the second element #} {% set secondTagArray = tags|slice:“1:2” %} {% if secondTagArray %}

<p>第二个标签（通过slice）：{{ secondTagArray[0]|trim }}</p>

{% else %}

<p>没有