While glancing through one of Narinda’s pull-requests, I noticed she’d used a syntax for dynamic classnames in Slim that I had not seen before:

/ Aww yeah
- dynamic_classname = (truthy_test ? 'foo' : 'bar')
.static-class-name-one class=["static-class-name-two", dynamic_classname]
  ' Foo or bar?

Slim will magically convert concatenate the classnames based on the truthiness of the truthy_test. Much more flexible (and less stinky) than the string concatenation I would usually use:

/ Eww
- dynamic_classname = (truthy_test ? 'foo' : 'bar')
.static-class-name-one class="static-class-name-two #{dynamic_classname}"
  ' Foo or bar?