oliveiragahenrique
Anonymous function style
I’m current learning Elixir by the book Elixir in Action 2nd Edition. On chapter 3 at Stream functions exercises i’ve solved them a bit different from the original repository.
Problem: Get the longest line length of a file
Book resoluiton:
def longest_line_length!(path) do
path
|> Stream.map(&String.replace(&1, "\n", ""))
|> Stream.map(&String.length/1)
|> Enum.max()
end
My resolution:
def longest_line_length!(path) do
File.stream!(path)
|> Stream.map(&String.replace(&1, "\n", ""))
|> Stream.map(&String.length(&1))
|> Enum.max()
end
Is there some fundamental difference between Stream.map(&String.length/1) and Stream.map(&String.length(&1)) ?
Or it is just a style preference?
Personally I think it’s more clear to use &1 even if it’s not necessary. Maybe it is just because I’m still getting used with the language. Any thoughts?
Marked As Solved
NobbZ
It’s not that that function is called twice, but it causes two function calls.
Using &f(&1) needs to first call the anonymous function which calls then the inner function call. Using &f/1 creates a more direct “reference” to the target function and therefore removes one level of indirection.
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Marcus
But something like this will be optimised by the compiler.
For example:
def foo(map) do
map
|> Enum.map(&String.upcase/1)
|> Enum.map(&String.upcase(&1))
end
becomes
foo(_map@1) ->
'Elixir.Enum':map(
'Elixir.Enum':map(_map@1, fun 'Elixir.String':upcase/1),
fun 'Elixir.String':upcase/1).
But &String.upcase/1 should be the preferred form.
shanesveller
Besides the points above, if you’re not reordering or transforming arguments before calling the existing function, the Mod.fun/arity style is more succinct to read and write, especially for functions with arity > 1. fun(&1, &2, &3) is repetitive in a way that isn’t productive.
srowley
I had the same reaction and preference when I first started learning Elixir. There may be some real difference between them that I am not aware of; I just think of it as a style difference.
Over time as I got accustomed to referring to a function as Module.function/arity, the former syntax (i.e. &String.length/1) became more natural and the latter started to feel redundant/unnecessary.
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