為什麼 deep_dup 實作卻只是呼叫 dup

[lulalala]

看 ActiveSupport 的 https://apidock.com/rails/Object/deep_dup

Returns a deep copy of object if it’s duplicable. If it’s not duplicable, returns self.

但是他的實作就只是呼叫

def deep_dup
  duplicable? ? dup : self
end

所以就只是 shallow copy 而已。

[tubaxenor]

應該要配合著https://github.com/rails/rails/blob/d66e7835bea9505f7003e5038aa19b6ea95ceea1/activesupport/lib/active_support/core_ext/object/duplicable.rb 看

#--
# 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.
#++

就可以理解deep_dup的目的應該是節省rescue的時間，至於naming為什麼要叫deep, 這個就...見仁見智吧