How do I create a mutable string in Ruby?

Question

I am using the # frozen_string_literal: true magic comment that RuboCop enforces by default, and I can't append something to a string:

string = 'hello'

string << ' world'

because it errors out with:

can't modify frozen String (RuntimeError)

Answer 1

You add a + before the string like:

string = +'hello'

string << ' world'

puts(string)

hello world

Answer 2

You can also use +=:

s = 'H'
s += 'ello

=> "Hello"