Monkey Patching

What is Monkey Patching in Ruby?

Monkey patching refers to reopening an existing class and changing its behavior by adding, modifying, or overriding methods. Ruby’s open classes make this possible, allowing developers to alter built-in classes (like String or Array) or third-party library code without changing the original source.

While powerful, monkey patching should be used carefully, as it can introduce unexpected behavior if not well managed.

Why is Monkey Patching Useful?

Monkey patching can be helpful in specific situations, such as:

• Fixing bugs in third-party libraries temporarily

• Extending core Ruby classes with missing functionality

• Adapting external code to fit application-specific needs

• Prototyping or experimenting quickly

It provides flexibility when traditional extension mechanisms (like inheritance or composition) are not practical.

How Monkey Patching Works?

In Ruby, classes can be reopened and modified at any time.

Example:

Adding a method to the String class

class String 
  
  def shout 
    
    upcase + "!" 
  
  end 

end 
 
"hello".shout 

# => "HELLO!"
  

This change affects all instances of String throughout the application.

Because of its global impact, Rails developers often prefer safer alternatives like modules, or Concerns when possible.

Where to Use Monkey Patching?

• Applying small, targeted fixes to third-party gems

• Adding backward compatibility during framework upgrades

• Legacy applications where refactoring is not feasible

• Controlled environments with clear documentation and tests

Monkey patching should be avoided in shared libraries or large teams unless absolutely necessary.

In Summary

Monkey patching allows Ruby developers to modify existing classes at runtime, offering great flexibility but also significant risk. When used carefully and sparingly, it can solve specific problems, but safer design patterns are usually preferred for long-term maintainability.