Enumerable.member-question-mark

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member?(enumerable, element)

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member?(t(), term()) :: {:ok, boolean()} | {:error, module()}

Checks if an element exists within the enumerable.

It should return {:ok, boolean} if you can check the membership of a given element in enumerable with ===/2 without traversing the whole of it.

Otherwise it should return {:error, __MODULE__} and a default algorithm built on top of reduce/3 that runs in linear time will be used.

When called outside guards, the in and not in operators work by using this function.