class BigDecimal

# File activesupport/lib/active_support/core_ext/object/duplicable.rb, line 111
def duplicable?
  true
end

BigDecimals are duplicable:

BigDecimal("1.2").duplicable? # => true
BigDecimal("1.2").dup         # => #<BigDecimal:...,'0.12E1',18(18)>