# Ruby Metaprogramming (Ruby on Rails)

> define_method, method_missing, class_eval, instance_eval, hooks, DSLs

- 20 interview questions
- Senior
- [Interview Questions: Ruby on Rails](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions.md)

## 1. What is metaprogramming in Ruby?

**Answer**

Metaprogramming is the ability of a program to write or modify code at runtime. In Ruby, this allows for dynamically defining methods, classes, and modules, making code more flexible and concise. This technique is widely used in frameworks like Rails to create elegant DSLs and reduce code duplication.

## 2. What is the purpose of the define_method method in Ruby?

**Answer**

define_method allows creating methods dynamically at runtime. It takes a method name (symbol or string) and a block defining the method body. Unlike def, define_method captures local variables from the enclosing scope via a closure, which is useful for generating methods with parameterized behaviors.

## 3. When is the method_missing method invoked by Ruby?

**Answer**

method_missing is called automatically when an object receives a method call that doesn't exist in its inheritance chain. It receives the name of the called method and its arguments, allowing dynamic handling of these calls. This is the foundation of many metaprogramming patterns like ghost methods used in ActiveRecord.

## 17 more questions available

- What is the main difference between class_eval and instance_eval?
- Which hook is called when a module is included in a class?

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## Other Ruby on Rails interview topics

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