Hi everyone, I have a function with two parameters with default values something like: def(param1 \\ %{}, param2 \\ "") do ### end this is the best practice for do that? or you know another way ?

You can also use functions from the Keyword module def foo(opts \\ []) do arg1 = Keyword.get(opts, :arg1, "default_value") ... end

I’ve learned the hard way that if you ever have more than one optional argument its a smell and you should refactor it to an opts list :smiley:

amazing! @srcoulombe and @zachdaniel thanks for you advice :slight_smile:

Absolutely never do this. Your colleagues or even your own future self will forget or be in a hurry just once and introduce a bug that would be difficult to track down. Either only one optional argument and it must 99% of the time be the last one – unless the differences in type will make it comple…

You have no idea how much I agree with this @zachdaniel , and it bites too many people in the butt too frequently. Maybe it should be part of the anti-patterns documentation!? [image] gushonorato: Or, using Keyword.validate!/2, would be better. I’ve been working with Elixir for a long time no…

[image] dimitarvp: Absolutely never do this. Your colleagues or even your own future self will forget or be in a hurry just once and introduce a bug that would be difficult to track down. Never say never :slight_smile: . If param2 depends on param1, I don’t see why not. Independent optional …

I don’t see why you’d need multiple default arguments for that? You can detect presence with keyword lists and derive defaults etc. Keyword.put_new_lazy(opts, :key, fn -> other_value = opts[:other_key] some_function_of(other_value) end)

I personally have found default arguments to be a good tool for trolling, as the default arguments are not restricted to the last arguments only as in many other languages, hence this is valid code too: def(param1 \\ %{}, param2 \\ "", param3, param4 \\ []) do # param3 is not optional end …

You know, it really bothers me knowing that KW lists require O(n) iteration over the list to extract the argument. I know full well that it will (almost) never matter in practice and I’m pretty sure it’s actually pushed down to native code, but I wince every time anyway… Of course, I still use them…

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Default arguments best practices?

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gushonorato March 11, 2025, 2:31pm 6

Or, using Keyword.validate!/2, would be better.