I have a new requirement on Array object. So I need to add my own method to built-in Array class.
How do I add a new method so that whatever Array object I create, it will also have my instance method?
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1Google "ruby open classes"Sergio Tulentsev– Sergio Tulentsev2013-07-25 13:04:01 +00:00Commented Jul 25, 2013 at 13:04
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2It's called monkey patching and it's done all the time. There's nothing special about the core classes that prevents you from adding methods to them.tadman– tadman2013-07-25 15:20:32 +00:00Commented Jul 25, 2013 at 15:20
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2 Answers
Use Ruby Open Classes:
class Array
def mymethod
#implementation
end
end
8 Comments
user2562153
If I do that my previous array objects don't get built in methods??
user2562153
They were objects of built-in Array and now became object of my new class called Array. So only method available to that object is the newly added instance method. For eg. uniq method is no longer working. When I do this object.methods all I see are my own module methods (where I defined the above class Array) and some methods of the module where the Array is originally defined. How do I get around?
Marek Lipka
@user2562153 It's not your new class. It's still the same
Array class, with all build in Array methods.user2562153
obj.class => # Class: X::Y::Z::Array, obj.methods => # Methods: ["==", "===", "=~", "id", "send", "class", "clone", "cy_rel_require", "display", "dup", "eql?", "equal?", "extend", "freeze", "frozen?", "hash", "id", "inspect", "instance_eval", "instance_of?", "instance_variable_defined?", "instance_variable_get", "instance_variable_set", "instance_variables", "is_a?", "kind_of?", "method", "methods", "my_contains_all?", "nil?", "object_id", "private_methods", "protected_methods", "public_methods", "respond_to?", "send", "singleton_methods", "taint", "tainted?", "to_a", "to_s", ...
the Tin Man
Then you're doing something wrong, but, because you have NOT included the code you're using in your question, we can't help fix it. That is why you have to include the code. This is a simple question and problem but YOU have to help us help you. As is, people will vote to close your question for lack of useful information.
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The other answers basically show you can add a method to the class by redefining the class, just to add to that, an example could be like this:
class Array
def third
size > 2 ? self[2] : nil
end
end
a = [1, 2, 3, 4, 5]
puts a.third
