I would usually be against introducing concepts to the core's standard
library that can be readily and easily expressed in user code.
However, in this case I think there are two strong arguments for including
the identity function in the standard library:
1. It is a great tool to help people new to functional programming with
their understanding.
2. It is a lot more clear in its purpose than `&(&1)` because it has a
name. (c.f. earlier operators vs named functions discussions).
~Marten/Qqwy
On Tuesday, July 2, 2019 at 11:23:47 AM UTC+2, Alexey Nikitin wrote:
>
> Like Haskell's `id` or Clojure's `identity` or Ruby's `itself`
>
> It can be very useful sometimes. Instead of writing ugly `&(&1)` it would
> much more attractive to write `&identity/1` or `&id\1`
> Moreover this function is already used as a default argument for some
> higher-order function. For example `Enum.group_by(enumerable, key_fun,
> value_fun \\ fn x -> x end)`
>
> Here are some examples
>
> ```
> #=> [1, 2, 3, true, 1234]
>
> 'abcdaabccc' |> Enum.sort |> Enum.chunk_by(&identity/1)
> #=> ['aaa', 'bb', 'cccc', 'd']
>
> [1, 1, 2, 3, 3, 1, 1, 5, 5] |> Enum.chunk_by(&identity/1) |>
> Enum.map(&hd/1)
> #=> [1, 2, 3, 1, 5]
>
> Enum.group_by('abracadabra', &identity/1)
> #=> %{97 => 'aaaaa', 98 => 'bb', 99 => 'c', 100 => 'd', 114 => 'rr'}
>
> Enum.map([1, 2, 3, 4], &identity/1)
> #=> [1, 2, 3, 4]
> [1,2,3,nil, true, false, 1234] |> Enum.filter(&identity/1)
> ```
>
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