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Comment by borromakot | Hacker News Reader

The point wasn’t to encourage shadowing bindings from a parent scope, only to illustrate that it is not the same thing as mutable references. Whether to, and when to, use rebinding is a different conversation, but in some cases it can lead to subtle bugs just like you described.

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I still think the difference to me as a programmer is largely semantic (except when the performance has to be considered): "rebinding" or "in-place mutation", in both cases it is a mutable variable to me.

There is a guarantee that you have when rebinding is the only option.

with rebinding:

    def thing() do
      x = 10
      do_something(x)
      # x is 10, non negotiably, it is never not 10
    end

with mutability

    def thing() do
      x = 10
      do_something(x)
      # who knows what x is? Could be anything.
    end

Additionally, because rebinding is a syntactic construct, you can use a linter to detect it: https://hexdocs.pm/credo/Credo.Check.Refactor.VariableRebind...

I find this a much better example than the example shown in the article. I even find it quite useful when explained like this.

Thanks!

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