Open Classes and Monkey Patching

Ruby allows modifying existing classes at runtime.

This feature, called 'Open Classes', enables developers to extend or change behavior dynamically.

What are Open Classes?

In Ruby, you can reopen and modify existing classes.

This allows adding new methods to built-in or user-defined classes.

Adding Methods to an Existing Class

Simply redefine a class and add new methods.

class String
  def shout
    self.upcase + '!!!'
  end
end

puts 'hello'.shout

Overriding Methods (Monkey Patching)

You can override existing methods in Ruby classes.

class String
  def reverse
    'Reversed method overridden!'
  end
end

puts 'hello'.reverse

Preserving the Original Method with super

Use super to keep the original method’s behavior.

class String
  def reverse
    super + ' (custom behavior added)'
  end
end

puts 'hello'.reverse

Use Cases for Open Classes

Open classes are useful in various scenarios:

• Extending built-in classes with additional methods.
• Enhancing third-party libraries.
• Improving readability and maintainability.

Risks of Monkey Patching

Monkey patching can be dangerous if not used carefully.

• Unexpected behavior when modifying core classes.
• Potential conflicts with third-party libraries.
• Harder debugging and maintainability.

Alternatives to Monkey Patching

Instead of modifying global behavior, consider using refinements.

Refinements allow modifying classes in a limited scope.

module StringExtensions
  refine String do
    def shout
      upcase + '!!!'
    end
  end
end

using StringExtensions
puts 'hello'.shout

Congratulations!

You have learned how to modify existing classes using Open Classes and Monkey Patching.

Next, you will explore how to use send and eval for dynamic method execution.