Ruby - method_missing Example

1. Introduction

Ruby, being a dynamic language, offers numerous metaprogramming capabilities. One such feature is the method_missing method. In this post, we'll dive into how to use method_missing to handle undefined methods dynamically.

Definition

The method_missing is a private method in Ruby's BasicObject class and is invoked when an object is sent a message (method call) it doesn't recognize. Instead of raising a NoMethodError, method_missing gives developers a hook to handle these unknown method calls in a customized manner.

2. Program Steps

1. Define a class that will employ method_missing.

2. Override the method_missing method in the class.

3. Introduce logic to handle specific unrecognized method calls.

4. Handle other unrecognized calls with a default behavior.

3. Code Program

class DynamicResponder
  # Method to handle undefined method calls
  def method_missing(method_name, *args, &block)
    if method_name.to_s.start_with?("say_")
      text = method_name.to_s.split("_")[1..-1].join(" ")
      puts text.capitalize
    else
      super  # Call the original method_missing in BasicObject
    end
  end
  # It's a best practice to override respond_to_missing? when method_missing is overridden
  def respond_to_missing?(method_name, include_private = false)
    method_name.to_s.start_with?("say_") || super
  end
end
responder = DynamicResponder.new
responder.say_hello_world
responder.say_ruby_is_awesome
responder.some_other_method

Output:

Hello world
Ruby is awesome
some_other_methods;: undefined method some_other_methods; for #<DynamicResponder:0x...> (NoMethodError)

Explanation:

1. We define a DynamicResponder class that will make use of method_missing.

2. Within the class, we override the method_missing method. This allows us to intercept calls to undefined methods.

3. We introduced a check for method names that start with "say_". If a method starts with this prefix, we split the method name into words, join them, and then print them out. This gives us dynamic behavior based on the method's name.

4. If the method doesn't match our criteria, we call the original method_missing from the BasicObject class using super, which raises a NoMethodError.

5. Additionally, when overriding method_missing, it's a best practice to also override respond_to_missing?. This ensures that respond_to? works correctly for our dynamic methods.

6. The example showcases this by calling two "say_" methods, which get handled dynamically, and one unrecognized method that raises a NoMethodError.

Using method_missing can be powerful, but it should be used judiciously. Overuse can lead to confusing code. Also, it can have performance implications since the handling of method calls through method_missing is slower than direct method calls.