Ruby, traditionally known as an Object-Oriented Programming (OOP) language, also offers a rich palette for those interested in the paradigms of Functional Programming (FP). In this blog post, we’ll explore how Ruby can be used to implement functional programming concepts, blending the best of both worlds.

Understanding Functional Programming

Functional Programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It emphasizes the application of functions, in contrast to the OOP approach which emphasizes objects.

Ruby’s Functional Facets

While Ruby is primarily an object-oriented language, it has several features that make functional programming possible and even enjoyable:

  1. Immutable Data Structures: Ruby’s core libraries, such as arrays and hashes, can be used in a functional style. You can perform operations on these data structures without altering their original state.
  2. First-Class Functions: Ruby treats functions (or methods) as first-class citizens, meaning you can store them in variables, pass them as arguments, and return them from other functions.
  3. Blocks, Procs, and Lambdas: These are Ruby’s tools for creating anonymous functions. They allow you to write code that is both expressive and functional.

Functional Techniques in Ruby

Here are some ways to incorporate functional programming techniques into your Ruby code:

  • Avoid Side Effects: Write functions that don’t alter the state outside of their scope. Instead of modifying global variables, return new values.
  • Use Map, Select, and Reduce: These methods are staples in functional programming. They transform, filter, and accumulate values from arrays and hashes without mutating the original data structure.
  • Leverage Lambdas and Procs: These allow you to encapsulate logic in a reusable, function-like manner.

Example: Functional Approach in Ruby

Here’s a simple example demonstrating a functional approach in Ruby:

# Define a lambda function
multiply_by_two = ->(x) { x * 2 }

# Apply the function to an array
numbers = [1, 2, 3, 4]
doubled_numbers =

puts doubled_numbers.inspect
# Output: [2, 4, 6, 8]

In this example, we define a lambda function to multiply a number by two and then apply this function to an array of numbers. The use of map ensures that we’re not modifying the original numbers array.


Ruby’s flexibility extends beyond OOP, allowing for a functional programming style that can lead to more readable, maintainable, and testable code. While Ruby might not be a pure functional language like Haskell or Erlang, it certainly provides enough functional features to enhance your programming toolkit. Embrace these capabilities, and you’ll discover a new, functional side of Ruby.