Don't mind me, just adding the equivalent ruby code for readers to compare:

    array.sort # returns a new collection

    array.sort! # sorts in place

(Ruby convention is to add a ! when methods directly modify the object they're called on.)

> Ruby convention is to add a ! when methods directly modify the object they're called on

No, Ruby convention is to add a “!” when there is a “less safe” version of an operation, for which a “more safe” version exists without a “!”.

Mutating versions of methods where a nonmutating version also exists are one common example, but not the only one, and mutating methods without a nonmutating counterpart don't get “!”.