Access syntax should raise when used on lists and key is not an atom

[ericmj]

list = [{0, "a"}]
list[0] # <= this does not raise
Keyword.get(list, 0) # <= this raises correctly

We can't check if the full list is correct because we use :lists.keyfind/3 for performance reasons, but we should at least check that the given key is an atom.

[liveforeverx]

Why it shouldn't be possible to use something else instead of atoms? For maps it is possible.

I'm not sure, but I think, that since this bug exists we use it for binary keys in lists.

[ericmj]

@liveforeverx Because Access is implemented for Keyword where only atoms are allowed for keys. Map is another data structure where any type is allowed for keys.

[liveforeverx]

@ericmj Understand, but it is a very synthetic restriction, which is not possible to overwrite, since Access is not protocol anymore.

This will transform code: data["key"] to something much more verbose: List.keyfind(data, "key", 0) if it used by many people... I'm not sure, if it used oft or not, or it is considered a bad style to get values but something else instead of atoms from tuple lists with Access protocol.

[ericmj]

@liveforeverx If you need a data structure that supports the access syntax and arbitrary types for keys you should use maps. This is an inconsistency in the language that should be fixed, this is the only place where keyword can be used with any type for the keys.

[josevalim]

What did we do on 1.0?

[ericmj]

What did we do on 1.0?

https://github.com/elixir-lang/elixir/blob/v1.0.0/lib/elixir/lib/access.ex#L48

[josevalim]

That settles it, thanks @ericmj.