I’d imagine by runtime check the author might have meant something like def function(%Island{} = island), where the alias quite literally shortens what you have to write in the parameter of the function.

The author is Lance Halvorsen @lance. He means that he is going to shorten the number of characters you have to type to write the code that happens to be a runtime check.

He’s not particularly active here, but he’s replied to you personally before Jan 18

My interpretation of the quoted statement is “runtime check” means pattern matching and “shorten” means typing fewer characters.

I probably should actually be more active here. I need more hours in the day, I guess.

We need to ask the author what they actually meant…

An alias does nothing but “renaming” an atom during compile time:

iex(1)> alias Foo, as: Bar
Foo
iex(2)> Bar === Foo
true
iex(3)> Bar
Foo