About variables scope

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Hello everybody,

I just noticed something that I admit I should have been notice way more earlier TBH..
Variables are scoped in ifs, conds, cases (and I bet it’s applicable to any block).

An example with a simplified snippet:

def doing_something do
  a = 1
  ...
  if some_true_condition do
    a = 2
    ...
  end
  IO.inspect(a)  # > Still 1 even if some_true_condition is true
end

Now I’m even surprised of how I didn’t got any bugs so far related to this behavior I wasn’t aware.
Maybe I’ve embraced FP well more than I think (so i’m glad).

But until now I didn’t come across (or maybe I didn’t notice) any resource explaining this behavior.
And it’s a really important behavior!

I searched on hexdocs.pm and looked on almost all the guides pages on elixir-lang and this is the only result I found, a changelog for version 1.3 where the following is stated:

Elixir will now warn if constructs like if , case and friends assign to a variable that is accessed in an outer scope.

And contrary to that there isn’t any warning anymore (on v1.10 btw).

I thought replacing the if construct by assigning from the whole block like so:

a =
  if some_true_condition do
    ...
    2
  end

But in this case we are still changing the value with nil if some_true_condition is actually false instead of doing nothing.

If you happen to have to do something equivalent (changing a value in a block) how do you handle it?
Also if you have any more information about this behavior, I’m interested to learn more.

Thank you!