What is Metaprogramming?

Metaprogramming is the ability of Ruby to modify its own structure at runtime.

It allows developers to dynamically define methods, change class behavior, and manipulate objects in powerful ways.

Ruby's Dynamic Nature

Unlike statically typed languages, Ruby allows you to modify classes and objects dynamically.

Methods, variables, and even classes can be created and modified at runtime.

Simple Metaprogramming Example

Using send, we can call methods dynamically.

class Person
  def greet
    'Hello!'
  end
end

p = Person.new
puts p.send(:greet)

Advantages of Metaprogramming

Metaprogramming allows for:

• Less repetitive code (DRY principle).
• More flexible and dynamic applications.
• Easy modifications and enhancements at runtime.

Where is Metaprogramming Used?

Metaprogramming is used in:

• Ruby on Rails (Active Record dynamically defines methods).
• DSLs (Domain-Specific Languages).
• Testing frameworks like RSpec.

Using instance_eval

instance_eval allows executing code in the context of an object.

class Person
end

p = Person.new
p.instance_eval { @name = 'Alice' }
puts p.instance_variable_get(:@name)

Using class_eval

class_eval dynamically modifies a class.

class Person
end

Person.class_eval do
  def greet
    'Hello!'
  end
end

puts Person.new.greet

Security Risks of Metaprogramming

Using metaprogramming can introduce security risks:

• Executing unknown code with eval can be dangerous.
• Overriding built-in methods can cause unexpected behavior.

Congratulations!

You have learned what metaprogramming is and how it allows dynamic modifications in Ruby.

Next, you will explore how to define and call methods dynamically.