Today I Learned ~D[2025-01-10]

Today’s TIL has a twist ending… so stick around.

Elixir has a shortcut for creating anonymous functions. I’ve always written:

greet = fn name -> "Hello, #{name}!" end 
# which can be invoked
greet.("Travis")
# returns
"Hello, Travis!"

However; I came across some tricky code with a case statement:

docs = case type do 
	:billing -> &[billing_act: &1]
    :shipping -> &[shipping_act: &1]
end 

# invocation
type = :billing
docs.("some customer")
# returns 
[billing_act: "some customer"]

This was very confusing to me, the fact that the anonymous function was a case form only further obfuscated what was happening. I thought it might be some case magic.

No. Apparently you can short cut the aforementioned anonymous function declaration:

greet = & "Hello, #{&1}!"

You treat this as any other anonymous function. You can even have multi-arity functions:

greet = & "Hello, #{&1} #{&2}!"
# invocation 
greet.("Travis", "Fantina")
# returns 
"Hello, Travis Fantina!"

In my case the case statement could have also been written:

docs = fn customer -> 
	case type do
		:billing -> [billing_act: customer]
    	:shipping -> [shipping_act: customer]
	end
end

Plot twist: This is not a TIL, apparently I learned this at least four years ago. That initial case function… the author was me four years ago!