Quick Answer

Metaprogramming technique to handle undefined methods.

Understanding the Issue

method_missing is called when an object receives a message it doesn't understand. It's powerful for DSLs and dynamic proxies.

The Problem

This code demonstrates the issue:

Ruby Error 
# Problem: Undefined methods
class User
  attr_accessor :name
end
user = User.new
user.first_name # NoMethodError

The Solution

Here's the corrected code:

Ruby Fixed 
# Solution: Dynamic handling
class User
  def method_missing(name, *args)
    if name.to_s.start_with?('first_')
      send(name.to_s.sub('first_', 'name'))
    else
      super
    end
  end
end

Key Takeaways

Use method_missing carefully and implement respond_to_missing?.