Adds &Kernel.identity/1 (#9182)

lib/elixir/lib/kernel.ex

@@ -482,6 +482,26 @@ defmodule Kernel do
     :erlang.floor(number)
   end
 
+  @doc """
+  Returns its argument.
+
+  ## Examples
+
+      iex> identity(17)
+      17
+
+      iex> identity(:ok)
+      :ok
+
+      iex> 'abcdaabccc' |> Enum.sort |> Enum.chunk_by(&identity/1)
+      ['aaa', 'bb', 'cccc', 'd']
+
+  """
+  @spec identity(a) :: a when a: var
+  def identity(a) do
+    a
+  end
+
   @doc """
   Returns the head of a list. Raises `ArgumentError` if the list is empty.