class RuboCop::Cop::Style::MutableConstant

Checks whether some constant value isn’t a mutable literal (e.g. array or hash).

Strict mode can be used to freeze all constants, rather than just literals. Strict mode is considered an experimental feature. It has not been updated with an exhaustive list of all methods that will produce frozen objects so there is a decent chance of getting some false positives. Luckily, there is no harm in freezing an already frozen object.

From Ruby 3.0, this cop honours the magic comment ‘shareable_constant_value’. When this magic comment is set to any acceptable value other than none, it will suppress the offenses raised by this cop. It enforces frozen state.

NOTE: ‘Regexp` and `Range` literals are frozen objects since Ruby 3.0.

NOTE: From Ruby 3.0, interpolated strings are not frozen when ‘# frozen-string-literal: true` is used, so this cop enforces explicit freezing for such strings.

NOTE: From Ruby 3.0, this cop allows explicit freezing of constants when the ‘shareable_constant_value` directive is used.

@safety

This cop's autocorrection is unsafe since any mutations on objects that
are made frozen will change from being accepted to raising `FrozenError`,
and will need to be manually refactored.

@example EnforcedStyle: literals (default)

# bad
CONST = [1, 2, 3]

# good
CONST = [1, 2, 3].freeze

# good
CONST = <<~TESTING.freeze
  This is a heredoc
TESTING

# good
CONST = Something.new

@example EnforcedStyle: strict

# bad
CONST = Something.new

# bad
CONST = Struct.new do
  def foo
    puts 1
  end
end

# good
CONST = Something.new.freeze

# good
CONST = Struct.new do
  def foo
    puts 1
  end
end.freeze

@example

# Magic comment - shareable_constant_value: literal

# bad
CONST = [1, 2, 3]

# good
# shareable_constant_value: literal
CONST = [1, 2, 3]