lib/backports/active_support/duplicable.rb

# Backport from Rails 4.x
# https://github.com/rails/rails/blob/4-0-stable/activesupport/lib/active_support/core_ext/object/deep_dup.rb

#--
# Most objects are cloneable, but not all. For example you can't dup +nil+:
#
# nil.dup # => TypeError: can't dup NilClass
#
# Classes may signal their instances are not duplicable removing +dup+/+clone+
# or raising exceptions from them. So, to dup an arbitrary object you normally
# use an optimistic approach and are ready to catch an exception, say:
#
# arbitrary_object.dup rescue object
#
# Rails dups objects in a few critical spots where they are not that arbitrary.
# That rescue is very expensive (like 40 times slower than a predicate), and it
# is often triggered.
#
# That's why we hardcode the following cases and check duplicable? instead of
# using that rescue idiom.
#++
class Object
  # Can you safely dup this object?
  #
  # False for +nil+, +false+, +true+, symbol, and number objects;
  # true otherwise.
  def duplicable?
    true
  end
end
class NilClass
  # +nil+ is not duplicable:
  #
  # nil.duplicable? # => false
  # nil.dup # => TypeError: can't dup NilClass
  def duplicable?
    false
  end
end
class FalseClass
  # +false+ is not duplicable:
  #
  # false.duplicable? # => false
  # false.dup # => TypeError: can't dup FalseClass
  def duplicable?
    false
  end
end
class TrueClass
  # +true+ is not duplicable:
  #
  # true.duplicable? # => false
  # true.dup # => TypeError: can't dup TrueClass
  def duplicable?
    false
  end
end
class Symbol
  # Symbols are not duplicable:
  #
  # :my_symbol.duplicable? # => false
  # :my_symbol.dup # => TypeError: can't dup Symbol
  def duplicable?
    false
  end
end
class Numeric
  # Numbers are not duplicable:
  #
  # 3.duplicable? # => false
  # 3.dup # => TypeError: can't dup Fixnum
  def duplicable?
    false
  end
end
require 'bigdecimal'
# rubocop:disable Lint/HandleExceptions
class BigDecimal
  begin
    BigDecimal.new('4.56').dup
    def duplicable?
      true
    end
  rescue TypeError
    # can't dup, so use superclass implementation
  end
end
# rubocop:enable Lint/HandleExceptions