Also commented below but the idea here was not actually mutation but safe and dangerous versions of methods... E.g, below insert is mentioned and it has no safe

Also commented below but the idea here was not actually mutation but safe and dangerous versions of methods... E.g, below insert is mentioned and it has no safer version so it has no ! version... Elixir adopted this convention from Ruby also, but there is never any mutation in Elixir of course as BEAM doesn't allow it.