Does using alias improve runtime speed on structs?


I am reading “Functional Web Development with Elixir, OTP and Phoenix” and in the book the author makes a surprising statement:

(…) In order to shorten that runtime check on an %Island{} struct, let’s add an alias at the top of the module file:
alias IslandsEngine.Island


Perhaps I am miss interpreting this, but what I understand is that by adding the alias of a struct to a module, we actually improve runtime speed on checks that use that struct.

I find this makes no sense at all. Using an alias only affects how the file is compiled, not how fast it runs on my machine.
Can someone explain this to me?

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
iex(2)> Bar === Foo
iex(3)> Bar
1 Like

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.


Yes, it shortens what I have to write, but as far as I know that has no runtime performance implications whatsoever.

This is why this paragraph seemed so odd to me.

I may be wrong, but he is not active in this forum, at least I don’t remember ever seeing him.

I’m not actually sure who the author is, therefore I used neutral “they”…

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.


Hi Everybody, :wave: :slight_smile:

Some of you have accurately interpreted the line already. To be extra clear, what I meant by “shorten” is “decrease the number of characters” and not “speed up”. Sorry for the confusion!


Thanks for the help!
I will remember that you are more active than I thought :stuck_out_tongue:

1 Like

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