Ruby String Mutability

Until Ruby 3 we need to explicitly call the method freeze on literal strings, so they become immutable. And, if you have a lot of literal strings in a file, this will be very repetitive and verbose. In order to let our code cleaner there is a magic comment that can be added in the top of each file.

the magic:

# frozen_string_literal: true

And it is done, all literal string are frozen now :)

example:

class Unfrozen
  def foo
    'bar'
  end
end

class StringFrozen
  def foo
    'bar'.freeze
  end
end

# frozen_string_literal: true
class ClassFrozen
  def foo
    'bar'
  end
end

To test that:

require 'spec_helper'

describe 'Ruby String Mutability' do
  it 'validates string mutability' do
    expect(Unfrozen.new.foo.frozen?). to be false
    expect(StringFrozen.new.foo.frozen?). to be true
    expect(ClassFrozen.new.foo.frozen?). to be true
  end
end

Randomized with seed 51265
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