A few Kotlin constructs have been introduced into the language over time. I wrote this post as a personal/public service advisory to remind us of their significance. Would love to credit img owner 1. fun interface (SAM) 1.1. (vs) function types 2. type alias 3. import alias 4. value class 5. data object Revisions 1. fun interface (SAM) Many languages (like Java) did not initially treat functions as first-class citizens.