Undefining a method in ruby removes an already defined method from a class or module. From within a module or a class, you can use Module#remove_method to remove a function's implementation, forcing Ruby to delegate to the superclass or a module included by a class.
Ruby has a unique keyword known as the undef keyword. This keyword is used to prevent working class members from responding to calls to the identified methods or variables that are supplied. You cannot invoke a method after using the under keyword with its name.
Code Solution
To add some randomization, I subclass Array in the code below and override the << and [] functions. When I realized that overriding [] wasn't a smart idea, I undefined that function to restore the Array behavior that was initially inherited. The overriding of << continues to apply.
Usually, a method is overridden by redefining it to implement the desired behaviour. However, a class can override an inherited method to do something you don't like, and you want the previous code back.
You can only use remove_method to remove a method from a class/module that explicitly defines it. To make a subclass stop responding to the inherited method, you should undefine the method with undef_method. The error will be there if we remove a method from a class that merely inherits that method.
Using undef_method on a class will prevent the appropriate method signals from reaching objects of that class, but it does not affect the parent class.
class RandomizingArray
remove(:length)
end
# NameError: method 'length' not defined
class RandomizingArray
undef_method(:length)
end
RandomizingArray.new.length
# NoMethodError: undefined method 'length' for []:RandomizingArray
Array.new.length # => 0
You can also try this code with Online Ruby Compiler
It is generally safer to use undef_method on the class you actually want to change than to use remove_method on its parent or a module it includes. You can use remove_method to remove singleton methods once they are used.
new_array = Array.new
def new_array.random_dump(number)
number.times { self << rand(100) }
end
new_array.random_dump(3)
new_array.random_dump(2)
new_array # => [6, 5, 2, 9, 66]
class << new_array
remove_method(:random_dump)
end
new_array.random_dump(4)
# NoMethodError: undefined method 'random_dump' for [6, 5, 2, 9, 66]:Array
You can also try this code with Online Ruby Compiler
When a method is defined on an object, Ruby silently defines an anonymous subclass used only for that one object. For example in the above code, new_array is actually an anonymous subclass of Array that implements a method random_dump.
Since the subclass has no name (new_array is a variable name), there's no way of using the class syntax and therefore we must "append" onto the definition of the new_array object.
Frequently Asked Questions
How to undefine a constant in Ruby?
In Ruby, we can use the Module#remove_constant method to undefine a constant and later it can be redefined with a different value.
How to undefine an instance variable in Ruby?
In Ruby, we can use the Object#remove_instance_variable method to remove an instance variable from a single instance of a class. Although, you can't remove a particular instance variable from all instances by modifying the class because the class is its own object.
What is the syntax for using undef?
The undef method can be used in the following manner: -
Type undef, followed by method name.
undef method_name
What is the defined keyword in Ruby?
The keyword defined is used to check whether the expression that is passed is defined or not. It will return a string describing its expression or argument if the passed expression or argument is defined.
What is the yield keyword in Ruby?
The provided expression is examined to see if it has been defined using the defined keyword. If the supplied expression or argument is defined, it will return a string that describes it.
Conclusion
In this article, we have extensively discussed how to undefine a method in Ruby and its implementation.
You can also check our previous blogs on Ruby Programming, Ruby Essentials, and Passing Arguments in Ruby. If you are eager to learn advanced front-end web development, Coding Ninjas is here with one of the best courses available, which you can find here.
116+ registered 