AssignWhen - use when clauses on assignment statements

Recently I was in a conversation with José Valim where I happened to mention that I find myself writing code like this:

X = if COND, do: Y, else: X

and that I wished I had some way to avoid the else boilerplate and make the code simpler. I asked him if there was some way I could write something like this:

X = Y IFF COND

He hummed and hawed for a minute and then pasted me the macro code that is now in the assign_when package on hex. This allows you to use when on assignment statements like this:

X = Y when COND

which is exactly equivalent to

X = if COND, do: Y, else: X

It works with tuples, and anything where you can say X = X. So for instance

{a,b} = {b,a} when a > b

should work fine. IMO avoiding the boilerplate like this makes for more elegant and more readable code. YMMV.

I want to repeat that I take no credit for this, the only thing I did was put release his hack to hex so people can use it. I personally think it would be a great addition to the language as a whole, but I am content to use it via a macro in this package. It uses some weird tricks that seem to cause my more experienced elixir colleagues to marvel over it, and I should note that it seems to confuse the ex_docs automagic on the docs page, but it works nicely so far for me. Thank you José!

https://github.com/demerphq/assign_when