frozen_string_literal

# Enable frozen string literal:
# in one file with magick comment: frozen_string_literal: true
# enable globally: RUBYOPT="--enable-frozen-string-literal"
a = "a"

# copies everything about an object in Ruby except for its frozen state
b = a.dup

# copy everything about and object in Ruby
c = a.clone

a.frozen? # => true
b.frozen? # => false
c.frozen? # => true

abc = String.new
abc.frozen? # => false

d = "ü"
d.force_encoding('UTF-8') # will raise an exception
d.dup.force_encoding('UTF-8') # will not raise an exception

e = "aaa"
e.gsub!("a", "b") # => will raise an exception
e.dup.gsub!("a", "b") # => will not raise an exception

buffer = ""
buffer << "String A" # => will raise an exception

# Alternative approach
buffer += "String A"
buffer # => String A

# However, if you use += you’re creating a new string on every call, and thus
# losing the advantage of the memory benefits of a single string. It’s much
# better to instead create a mutable copy of the initial string via the dup
# method:
buffer = "".dup
buffer << "String B"
buffer # => String B

# Helpful sources:
# A command line interface for managing/formatting source file directive pragma comments (a.k.a. magic comments).
# https://github.com/bkuhlmann/pragmater

# Rubocop:
# https://rubocop.readthedocs.io/en/latest/cops_style/#stylefrozenstringliteralcomment