In this post I discuss what immutability means in the context of Elixir, and the properties that stem from it.
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This mutation, however, is syntactic.
Wish I’d been armed with this simple explanation in some past discussions 
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A bit more explanation would be: each variable points to an exclusive memory location which can not be mutated. A new variable (even when named the same) is a new exclusive memory location.
The blog does a good job of explaining that Elixir numbers the variable names internally, so the second ‘varname’ is in fact ‘varname2’ underneath and so no the same variable.
Nitpick: The example with the rookie mistake is not that clear at first sight. @zachdaniel might want to either explain it a bit more why it does “ surprising stuff” or replace it with another variant, as for me it does exactly what I expect it to do (just not from an immutable view). One that bit myself once: have a list of date ordered scores [1,5,2], send it to function top_score to pick the top score by sorting [1,2,5] it and give me the top result 5, continue with the list below the call to top_score(list) expecting it to be the original date sorted [1,5,2]….auch. In this example the function was never expected to mess up the list order ‘globally’.
As Javascript is large in React, the sorting function would cause a unexpected rerender due to the change.
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Very nicely written. To summarize: Mutation depends on the point of view; Unobservable mutations do not count; Mutations can only be observed through indirect observation, such as an impure function call.
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Oh I meant to have it handy as a retort to those who claim that Elixir is essentially mutable due to re-assignment. As the post states it’s arguable, but “syntactically mutable” is a clear distinction. Thinking back on it, I think that was basically the other person’s argument but neither of us were being very eloquent.
