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#--
# 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+, symbols, numbers, class and module 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
class Class
# Classes are not duplicable:
#
# c = Class.new # => #<Class:0x10328fd80>
# c.dup # => #<Class:0x10328fd80>
#
# Note +dup+ returned the same class object.
def duplicable?
false
end
end
class Module
# Modules are not duplicable:
#
# m = Module.new # => #<Module:0x10328b6e0>
# m.dup # => #<Module:0x10328b6e0>
#
# Note +dup+ returned the same module object.
def duplicable?
false
end
end
require 'bigdecimal'
class BigDecimal
begin
BigDecimal.new('4.56').dup
def duplicable?
true
end
rescue TypeError
# can't dup, so use superclass implementation
end
end
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