How can I describe mutable strings when strings are immutable by default?

Question

When a file has the pragma:

# frozen_string_literal: true

all strings written as literals in that file are frozen by default. When I want my strings to be immutable overall, and hence am using the pragma, but want to have a couple of mutable strings, what is the recommended way to write them?

All I can think of is:

String.new("foo")

Answer 1

I had missed it. The recommended way is to use the +@ method string literal.

(+"foo").frozen? # => false
(-"foo").frozen? # => true
"foo".frozen? # => true