Shopify’s native support of arrays is… Iffy at best, completely inadequate at worst.

There are workarounds for most standard operations, and I’m going to keep a list of them here for personal reference and for whomever they might be useful for.

Declare Empty Array

Copilot and other code-completion engines autocomplete this code snippet:

{% liquid 
    assign descriptions = []
%}

But in liquid we have to use the split operator on an empty string like so:

{% liquid
    assign descriptions = '' | split: ''
%}

Append Array Item

Again code engines will autocomplete this snippet:

{% liquid     
    assign description = block.settings.description
    assign descriptions = descriptions | push: description
%}

In Shopify Liquid there is no push filter, this comes from Jekyll.
Instead, we need to use a combination of the sort filter and the concat filters.
This trick comes from Dave Warrington’s Blog.

{% liquid
    assign description = description | sort
    assign descriptions = descriptions | concat: description
%}

Here we are using the sort filter to create an array of 1 item.
Once we have that we concat it with the original array.