Twig, add first and last class

Question

Let's say I have a for loop like this:

{% for elem in arrMenu %}
    <div class="topmenu-button">
        <a href="{{ elem.url }}">{{ elem.name }}</a>
    </div>
{% endfor %}

In that form, it would render something like:

<div class="topmenu-button"><a href="url">name</a></div>
<div class="topmenu-button"><a href="url">name</a></div>
<div class="topmenu-button"><a href="url">name</a></div>
<div class="topmenu-button"><a href="url">name</a></div>

How can twig help me to add first and last classes the the div, so that I would have a result like:

<div class="topmenu-button first"><a href="url">name</a></div>
<div class="topmenu-button"><a href="url">name</a></div>
<div class="topmenu-button"><a href="url">name</a></div>
<div class="topmenu-button last"><a href="url">name</a></div>

Answer 1

You can use the "special variables" loop.first and loop.last for what you want.

LINK

{% for elem in arrMenu %}
    {% if loop.first %}
    <div class="topmenu-button first">        
    {% elseif loop.last %}
    <div class="topmenu-button last">        
    {% else %}
    <div class="topmenu-button">        
    {% endif %}
        <a href="{{ elem.url }}">{{ elem.name }}</a>
    </div>
{% endfor %}

EDIT: depending how much you care about the "one case", you might need a solution like this.

{% for elem in arrMenu %}
    {% set classes = ["topmenu-button"] %}
    {% if loop.first %}{% set classes = classes|merge(["first"]) %}{% endif %}
    {% if loop.last %}{% set classes = classes|merge(["last"]) %}{% endif %}
    <div class="{{ classes|join(" ") }}">        
        <a href="{{ elem.url }}">{{ elem.name }}</a>
    </div>
{% endfor %}