Using 'or' in Liquid for optional template variable

Question

I have a small Jekyll-powered site that uses the default Liquid templating engine. I'm converting it to use Gekyll, which overrides the standard page.date template variable with a Git timestamp, so I need to override the date with a page.original_date value declared in the front matter just for older posts.

In my template, I'd like to be able to do this:

<span class="date">{% page.original_date or page.date | date: "%B %-d, %Y" }}</span>

That doesn't appear to work, so I'm doing this:

<span class="date">
{% if page.original_date %}
    {{ page.original_date | date: "%B %-d, %Y" }}
{% else %}
    {{ page.date | date: "%B %-d, %Y" }}
{% endif %}
</span>

It's not a big deal, but cumbersome enough to look for a better solution. Does the logic in Liquid allow for a fallback variable like in my first attempt?

Answer 1

In terms of looking for a ternary operator, I think this is the simplest syntax you can use:

{% assign original_date = page.original_date %}
{% unless original_date %}{% assign original_date = page.date %}{% endunless %}
{% unless original_date %}{% assign original_date = date: "%B %-d, %Y" %}{% endunless %}

Not very readable or concise, but at least it works!

Answer 2

{% page.original_date or page.date | date: "%B %-d, %Y" }} logic isn't correct to me in the first place.

or operator is definitely supported in Liquid, but it is a conditional-OR operator performing a logical-OR like other normal programming languages.

However, what you want to is a fallback thing, like ternary operator.

For example, similarly to C#'s ?? Operator or ?: Operator

{% page.original_date ?? page.date | date: "%B %-d, %Y" }}
{% page.original_date ? page.original_date : page.date | date: "%B %-d, %Y" }}

Unfortunately, I don't think it exists in Liquid. See this Ternary operator support isssue at Liquid's issue tracker.