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* doc/syntax/modules_and_classes.rdoc: Added singleton classes

documentation.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38710 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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drbrain 2013-01-05 20:35:30 +00:00
parent 902a36c1f6
commit ac67a2b6d4
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@ -1,3 +1,8 @@
Sun Jan 6 05:35:18 2013 Eric Hodel <drbrain@segment7.net>
* doc/syntax/modules_and_classes.rdoc: Added singleton classes
documentation.
Sun Jan 6 02:22:00 2013 Zachary Scott <zachary@zacharyscott.net>
* lib/webrick/httpservlet/abstract.rb (WEBrick::HTTPServlet): Typo in

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@ -291,3 +291,48 @@ provide them manually like <code>super(2)</code>.
+super+ may be called as many times as you like in the subclass method.
= Singleton Classes
The singleton class (also known as the metaclass or eigenclass) of an object is
a class that holds methods for only that instance. You can access the
singleton class of an object using <code>class << object</code> like this:
class C
end
class << C
# self is the singleton class here
end
Most frequently you'll see the singleton class accessed like this:
class C
class << self
# ...
end
end
This allows definition of methods and attributes on a class (or module) without
needing to write <code>def self.my_method</code>.
Since you can open the singleton class of any object this means that this code
block:
o = Object.new
def o.my_method
1 + 1
end
is equivalent to this code block:
o = Object.new
class << o
def my_method
1 + 1
end
end
Both objects with have a +my_method+ that returns +2+.