`tap` is one of my favorite #Elixir functions. I implemented it myself in my #Uptight functools, but then a colleague of mine told me that it's already in #Kernel.

Documentation: https://hexdocs.pm/elixir/1.12.3/Kernel.html#tap/2

Code: https://github.com/elixir-lang/elixir/blob/v1.12.3/lib/elixir/lib/kernel.ex#L1160