From 2ddbef421cb877bc219ac2737bbba793c53edbde Mon Sep 17 00:00:00 2001 From: Xavier Noria Date: Thu, 19 Nov 2009 00:10:19 +0100 Subject: explains the motivation for duplicable? --- .../lib/active_support/core_ext/object/duplicable.rb | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'activesupport/lib/active_support/core_ext/object/duplicable.rb') diff --git a/activesupport/lib/active_support/core_ext/object/duplicable.rb b/activesupport/lib/active_support/core_ext/object/duplicable.rb index a2d4d50076..b05325790c 100644 --- a/activesupport/lib/active_support/core_ext/object/duplicable.rb +++ b/activesupport/lib/active_support/core_ext/object/duplicable.rb @@ -1,3 +1,19 @@ +# 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. -- cgit v1.2.3