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Description: Ruby on Rails
Homepage: http://rubyonrails.org
Clone URL: git://github.com/rails/rails.git 
Added Object#metaclass
josh (author)
Tue Jul 15 19:24:00 -0700 2008
commit  f4f6e57e8c2a446a4a600576f0caf0fb8921ba13
tree    e3541a545c85cc00a5182532b4c2b6d9376c815d
parent  89eec91e670ae267cd88b2b3555bfefe527f0eaa
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activesupport/lib/active_support/core_ext/object.rb 
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@@ -1,4 +1,5 @@
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 require 'active_support/core_ext/object/conversions'
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 require 'active_support/core_ext/object/extending'
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 require 'active_support/core_ext/object/instance_variables'
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+require 'active_support/core_ext/object/metaclass'
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 require 'active_support/core_ext/object/misc'
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activesupport/test/core_ext/object_and_class_ext_test.rb 
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@@ -173,6 +173,14 @@ class ObjectTests < Test::Unit::TestCase
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     assert duck.acts_like?(:time)
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     assert !duck.acts_like?(:date)
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   end
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+
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+  def test_metaclass
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+    string = "Hello"
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+    string.metaclass.instance_eval do
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+      define_method(:foo) { "bar" }
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+    end
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+    assert_equal "bar", string.foo
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+  end
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 end
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 class ObjectInstanceVariableTest < Test::Unit::TestCase

Comments

anildigital Sun Jul 20 05:32:08 -0700 2008

Hey.. any strong example, where I could use metaclass in a rails app?

nakajima Sun Jul 20 07:06:14 -0700 2008

It’s really useful when it comes to metaprogramming in Ruby.

ryanb Sun Jul 20 08:12:17 -0700 2008

Jay Fields has a blog post on the subject. He explains some pros and cons of this approach.

smtlaissezfaire Sun Jul 20 10:08:17 -0700 2008

Why isn’t rails using the facets gem?

josh Sun Jul 20 11:17:20 -0700 2008

Why isn’t facets using activesupport? :)

NZKoz Sun Jul 20 11:50:16 -0700 2008

@anildigital: I’ve you’ve never felt you needed it, you probably don’t :)

nakajima Sun Jul 20 12:00:48 -0700 2008

I wanted to be a bit more helpful above but I was posting from my iPhone. why the lucky stiff has a great post about metaclasses here. The metaclass method is a great help for handling per-object things in your app. It can be over-used, but it can also help you do fun things like this.

nakajima Sun Jul 20 12:02:02 -0700 2008

Actually, the example I posted is just a convoluted example of something that can be done a million other ways. The good thing is that once you get a handle on the notion of metaclasses and such, you’ll know when and when not to use it. :)

cpjolicoeur Mon Jul 21 17:40:06 -0700 2008

glad this has finally been folded in so everyone does have to define this method themself

hoverbird Fri Jul 25 17:05:03 -0700 2008

I liked this snippet best the first time I saw it….. when it was on the back of _why’s Ruby Kaigi 2007 t-shirt. or in metaid.rb

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