Twig - use the value of a variable as a hash key

twig-variable-array-key.twig

{% set foo = "myKey" %}
{% set bar = "my value" %}

{# To name a hash key with the value of the foo variable, wrap the variable in parentheses: #}
{% set newThing = {(foo): bar} %}

{# Which is the same as #}
{% set newThing = {myKey: "my value"} %}